JP6503210B2 - Control device - Google Patents

Description

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

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

  Therefore, there is known one that detects the oxygen concentration in the exhaust gas with an air-fuel ratio sensor and performs feedback control of the amount of fuel supplied to the internal combustion engine. For example, Patent Document 1 discloses a technique for feedback control of a fuel supply amount to an internal combustion engine based on an air-fuel ratio detected by an air-fuel ratio sensor.

JP 2001-318074 A

  However, if the air-fuel ratio sensor or the air-fuel ratio controller generates an overcurrent due to a ground fault or a rush current at startup, feedback control based on the overcurrent is performed, making it difficult to derive an appropriate fuel supply amount. Become. For example, when the fuel supply amount is derived based on the excess current, an excessive or excessively small fuel supply amount may be derived, which may significantly reduce the exhaust gas purification efficiency. Also, when feedback control based on overcurrent is performed, the value used in feedback control is calculated to an excessive value, and the overcurrent is ended until the value of the normal state is restored. There is a possibility that the air-fuel ratio sensor or the controller may be erroneously determined to have an abnormality.

  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 problems, the invention according to claim 1 relates to a detection cell unit that generates an air-fuel ratio voltage according to an air-fuel ratio, and oxygen according to the amount of current that is connected with the detection cell unit and connected. A control unit for controlling an air-fuel ratio sensor provided in an exhaust unit of an internal combustion engine, the pump unit including: a pump cell unit for sucking and discharging the gas; and output means for outputting an output voltage based on the air-fuel ratio voltage; Based on the above, an energizing means for energizing the pump cell portion with a pump current so that the air-fuel ratio becomes a predetermined ratio, and a constant voltage means for controlling the connecting portion voltage generated at the connecting portion to a predetermined specified voltage value And limiting means for limiting the value of the pump current so that the value of the pump current does not exceed the range of a predetermined current value. The range of the predetermined current value is that the constant voltage means has the connection voltage and the specified voltage value. Within the specified range Area by Der possible.

The invention according to claim 2 is the control device according to claim 1, wherein the limiting means limits the value of the output voltage of the output means so as not to exceed the range of a predetermined voltage value. The current value is limited so as not to exceed the predetermined current value range .

The invention according to claim 3 further comprises a first detection means for detecting the voltage at the connection portion in the control device according to claim 1, wherein the restriction means is the connection portion by the first detection means. When it is detected that the voltage is higher or lower than the specified voltage value by a predetermined value or more, the value of the output voltage of the energizing means is restricted so that it does not exceed the range of the predetermined voltage value. The current value is limited so as not to exceed the predetermined current value range .

The invention according to claim 4 relates to the control device according to claim 1, wherein a resistor connected between the connecting portion and the constant voltage means, a connection point between the resistor and the constant voltage means A second detection means for detecting a connection point voltage generated at the second detection means, wherein the second detection means detects that the connection point voltage is higher or lower than a predetermined voltage value. In this case, the value of the pump current is limited so as not to exceed the predetermined current value range by restricting the value of the output voltage of the energizing means not to exceed the predetermined voltage value range .

The invention according to claim 5 comprises the control device according to any one of claims 1 to 4 and control means for controlling a fuel injection valve for injecting fuel to the internal combustion engine, the control means comprising fuel comprising: a receiving means for receiving the value of the pump current, a first derivation means for deriving the air-fuel ratio from the value of the pump current, and a second deriving means for deriving the injection amount of the fuel based on the air-fuel ratio, the it is an injection apparatus.

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

  Further, according to the invention of claim 2, in particular, the limiting means limits the value of the output voltage not to exceed the predetermined voltage value, so that the limiting means can limit the value of the pump current in an appropriate manner.

  Further, according to the third aspect of the invention, since the limiting means controls the energizing means in accordance with the value of the connection voltage, the limiting means can limit the value of the pump current based on the accurate voltage value.

  Further, according to the invention of claim 4, in particular, since the limiting means controls the energizing means in accordance with the value of the connection point voltage, the limiting means can limit the value of the pump current based on the voltage value of the appropriate place. .

In particular, according to the invention of claim 5 , since the limiting means limits the value of the pump current so that the value of the pump current does not exceed the predetermined current value, the control means can derive an appropriate fuel injection amount and inject it from the fuel injection valve. .

FIG. 1 is a schematic view 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 showing an example of the correlation between the excessive pump current and the COM voltage. FIG. 4 is a view showing the configuration of the air-fuel ratio control device according to the first embodiment. FIG. 5 is a diagram showing the configuration of the limiting circuit. FIG. 6 is a view showing the configuration of an air-fuel ratio control device according to a second embodiment. FIG. 7 is a diagram showing the 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 an internal combustion engine 10a. The air-fuel ratio control system 10 controls the fuel injection device 3 including the air-fuel ratio sensor 2 and the air-fuel ratio control device 1 and the fuel injection valve 4 so that the fuel burned in the internal combustion engine 10a becomes near the theoretical air-fuel ratio Control. A lean (lean) air fuel ratio of fuel advantageous for fuel consumption and a rich air fuel ratio of fuel used at the time of start or acceleration are also used, and the air fuel ratio can be used properly depending on the load condition. Therefore, feedback control of the air-fuel ratio is always performed while the internal combustion engine 10a is being driven.

  First, 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 and 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 the 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 Perform feedback control so that

  In such feedback control, the air-fuel ratio sensor 2 is disposed in the exhaust pipe 10d, and outputs a signal according to the oxygen concentration in the exhaust gas. The air-fuel ratio sensor 2 includes a detection cell unit 2a that can linearly detect an air-fuel ratio, and a pump cell unit 2b that sucks and discharges oxygen. By pumping the pump cell portion 2b and matching the air-fuel ratio detected by the detection cell portion 2a with the theoretical air-fuel ratio, it is possible to detect the difference between the air-fuel ratio detected by the detection cell portion 2a and the theoretical air-fuel ratio. By detecting such a difference, it is possible to detect the air-fuel ratio of the exhaust gas in the exhaust pipe 10d.

  Further, 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 become excessively large or smaller than predetermined values.

  FIG. 2 shows the configuration of a conventional air-fuel ratio control device 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 portion 2a of the air-fuel ratio sensor 2 (a terminal provided on the opposite side to the side where the detection cell portion 2a is connected to the pump cell portion 2b). In the case of a voltage corresponding to the stoichiometric air fuel ratio, 0.45 [V] is generated at the VS terminal. Therefore, when the exhaust pipe is at the theoretical air fuel ratio, the voltage at the VS terminal becomes 3.75 [V] by adding the voltage at the connection portion between the detection cell portion 2a and the pump cell portion 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.

  The VI conversion circuit 120 pumps 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 based on the voltage value output from the A / F detection circuit 110. Energize. That is, the VI conversion circuit 120 applies a pump current Ip of a value at which the pump cell unit 2b should pump oxygen to the pump cell unit 2b so as to fill the difference between the detected air-fuel ratio and the theoretical 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, it is 3.3 [V].

  The constant voltage control unit 130 applies a COM current Icom to the sense resistor Rs, which is a resistor, and generates a voltage drop in the sense resistor Rs, thereby controlling the connection terminal com to have a constant voltage value. That is, the constant voltage control unit 14 controls the voltage (COM terminal voltage Vcom; connection portion voltage) generated at the connection terminal com, which is the connection portion between the detection cell portion 2a and the pump cell portion 2b, to a constant specified voltage value. Do. In addition, the current capability which can control the connection terminal com to a fixed voltage value by the constant voltage control part 14 supplying the COM current Icom is determined by the following equation. The current capability is the capability to conduct 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 a 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 at which the output of constant voltage control unit 14 is limited and COM terminal voltage Vcom.

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

  Here, in the control device 100 of such an air-fuel ratio, if an over-current Is due to a ground fault or a rush current at the time of start is generated 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 portion), 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 rises, the voltage generated at the VS terminal also rises. 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 occurrence of the overcurrent Is continues or increases, the feedback control of the air-fuel ratio is repeated, so that the pump current Ip becomes further excessive.

  The constant voltage control unit 140 can hold the COM terminal voltage Vcom at a constant voltage as long as the value of the pump current Ip is within the range that the current capability of the constant voltage control unit 140 allows. However, when 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 feedback control is performed after the end of the overcurrent, the pump cell portion 2b is supplied with an excessive pump current Ip despite the end of the overcurrent. If an excessive current is supplied to the pump cell portion 2b in a normal state, it may be erroneously determined as an abnormal state of the air-fuel ratio sensor 2, and control may be impaired.

  FIG. 3 shows the correlation between the excessive pump current Ip and the COM terminal voltage Vcom. The COM terminal voltage Vcom is controlled to 3.3 [V] by the constant voltage control unit 140 until the pump current Ip is, for example, about 30 [mA]. However, when the pump current Ip exceeds 30 [mA], the COM terminal voltage Vcom rises 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 can not control the COM terminal voltage Vcom to 3.3 [V]. That is, the constant voltage control unit 140 can apply the COM current Icom to the sense resistor Rs, and the total amount of current including the pump current Ip applied to the connection terminal com can not be reduced to 30 [mA] or less. . 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 return a plurality of calculations before returning to 3.3 [V] by feedback control.

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

<1-2. Configuration>
FIG. 4 shows the configuration of the air-fuel ratio control device 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 31 a, an air-fuel ratio deriving unit 31 b, and a fuel deriving unit 31 c, and controls the fuel injection valve 4.

  The receiving unit 31 a 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-area 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 of a solid electrolyte material such as zirconia having oxygen ion conductivity, and is disposed in an exhaust pipe. The air-fuel ratio sensor 2 includes a heater, an atmosphere chamber, and a gas diffusion chamber (all not shown). Further, the air-fuel ratio sensor 2 includes a detection cell unit 2a and a pump cell unit 2b which are 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 to activate the air-fuel ratio sensor 2. The atmosphere chamber is formed in communication with the atmosphere outside the exhaust pipe, and takes in the atmosphere serving as the reference gas into the air-fuel ratio sensor 2. The gas diffusion chamber is formed in communication with the exhaust gas by an exhaust introduction hole formed in the air-fuel ratio sensor 2, and takes the exhaust gas into the air-fuel ratio sensor 2.

  The detection cell unit 2a is also referred to as a Nernst cell, and generates a voltage (air-fuel ratio voltage) according to the air-fuel ratio of the exhaust gas in the exhaust pipe. The detection cell unit 2a generates, at the terminal VS, a voltage according to the oxygen ion concentration in the gas diffusion chamber. By detecting the voltage generated in the detection cell portion 2a, it is possible to detect the difference (deviation) between the air fuel ratio of the exhaust gas and the theoretical air fuel ratio.

  The pump cell unit 2b sucks and discharges oxygen according to the supplied current (pump current Ip). The pump cell unit 2b sucks and discharges oxygen so that the detection cell unit 2a detects the stoichiometric air fuel ratio. Therefore, if the current is detected, the deviation of the exhaust gas from the air-fuel ratio can be detected, and the air-fuel ratio in the exhaust pipe can be detected from the magnitude of the deviation. The pump cell unit 2b has a terminal IP on the opposite side connected to the detection cell unit 2a. Pump current Ip is applied to terminal IP.

  Note that the direction of voltage application to the pump cell portion 2b is reversed based on the lean / rich output in the detection cell portion 2a, so that the current flowing through the pump cell portion 2b is wide in both the lean region and the rich region. It becomes possible to detect the air-fuel ratio.

  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 monitoring 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 a limiting 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 limits in the range of a predetermined value of 6.5 [V] to 1.0 [V]. That is, the limiting circuit 12 functions as limiting means for limiting the value of the pump current Ip not to exceed the predetermined current value by limiting the value of the output voltage to the predetermined voltage value (6.5 [V] or less). 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 theoretical 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 deviation between the air fuel ratio of the exhaust gas and the theoretical air fuel ratio. The pump current Ip is supplied based on the air-fuel ratio state, ie, rich or lean, so when supplied from the terminal IP side to the connection terminal com side or supplied from the connection terminal com side to the terminal IP side May be The VI conversion circuit 13 functions as an energizing unit for energizing the pump cell portion 2b with the pump current Ip so that the air fuel ratio becomes a predetermined ratio.

  The constant voltage control unit 14 controls the connection terminal com to be constant at a predetermined voltage value (for example, 3.3 [V]) by supplying a current to the sense resistor Rs to generate a voltage. 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, a current that the constant voltage control unit 14 applies to the sense resistor Rs is referred to as a COM current Icom. In addition, since the COM current Icom is energized based on the voltage (connection voltage) of the connection terminal com, the case where current is applied from the constant voltage control unit 14 side to the connection terminal com side, and the constant voltage from the connection terminal com side The control unit 14 may be energized. 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 specified 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 range of predetermined upper limit value and lower limit value, 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 supplied to the pump cell unit 2b by the VI conversion circuit 13 is smaller than the COM current Icom supplied to the sense resistor Rs by the constant voltage control unit 14. That is, the limiting circuit 12 limits the voltage value output from the A / F detection circuit 11 to the VI conversion circuit 13 such that COM current Icom> pump current Ip. As a result, even when the pump current Ip is increased by feedback control based on the overcurrent, the pump current Ip can be limited to less than the COM current Icom. Then, after the termination of the overcurrent, the constant voltage control unit 14 can control the connection terminal com to a predetermined voltage (for example, 3.3 [V] as described above) promptly.

  As a result, even if an excess current occurs 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 limiting circuit 12. The conversion circuit 13 does not excessively reduce the pump current Ip. As a result, since the voltage output from the constant voltage control unit 14 can be kept within an appropriate range, feedback control of the air-fuel ratio 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 monitoring unit 15 is transmitted to a control unit 31 described later, and the control unit 31 calculates an air-fuel ratio and a fuel injection amount.

  The control unit 31 acquires the value of the pump current Ip from the current monitoring 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 a value of the pump current Ip, an air-fuel ratio deriving unit 31b that derives an air-fuel ratio from the value of the pump current Ip, and a fuel deriving unit 31c that derives the injection amount of the fuel based on the air-fuel ratio. Equipped with The receiving unit 31a functions as a "receiving unit", the air-fuel ratio deriving unit 31b functions as a "first deriving unit", and the fuel deriving unit 31c functions as a "second deriving unit".

  FIG. 5 shows the detailed configuration of the limiting circuit 12. The limiting circuit 12 comprises three operational amplifiers OP1, OP2 and OP3. The operational amplifiers (OP1, OP2, and OP3) are operational amplifiers that output, from an 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.

  The operational amplifier OP1 has a non-inverted input terminal NI1 connected to the A / F detection circuit 11, an inverted input terminal II1 connected to the reference power supply Vref1, and an output terminal OUT1 connected to the VI conversion circuit 13. The voltage output by 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 by 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 by 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].

  Thus, the voltage input from the A / F detection circuit 11 to the non-inversion input terminal NI1 of the operational amplifier OP1 is output to the VI conversion circuit 13 with its upper limit and lower limit limited by the limit circuit 12. As a result, an overcurrent is generated in the control device 1 or the air-fuel ratio sensor 2 to increase the COM terminal voltage Vcom, and the A / F detection circuit 11 receives the increased voltage of the terminal VS. The voltage output from the detection circuit 11 to the VI conversion circuit 13 will not be excessive. Therefore, the pump current Ip output from the VI conversion circuit 13 does not become excessive, and stable feedback control of the air-fuel ratio can be promptly performed using the pump current Ip even after the termination 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 feedback control a plurality of times until the pump current Ip is reduced to a normal value. In this case, quick feedback control can not be performed. In addition, while the pump current Ip is reduced to a normal value, the excessive pump current Ip may be erroneously determined to be abnormal despite the normal state in which the overcurrent has ended.

  As described above, the control device 1 according to the first embodiment limits the value of the pump current Ip not to exceed the current value in the predetermined range. For this reason, since the pump current Ip does not become excessive or excessively small, the air-fuel ratio sensor 2 and the control device 1 are not erroneously determined to be abnormal. Moreover, since the period which transfers to a normal state can be shortened by feedback control after the end of an overcurrent, the erroneous abnormality detection by the abnormal value in a 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 stably controlled promptly based on the value of the pump current Ip.

<2. Second embodiment>
Next, a second embodiment will be described. The second embodiment includes the same configuration as the first embodiment. Therefore, the differences from the first embodiment will be mainly described.

  FIG. 6 shows the configuration of the air-fuel ratio control device 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 between the connection terminal com and the VI conversion circuit 13. And a voltage monitor unit 16. Further, 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 puts the input voltage in a predetermined range and outputs it.

  The voltage monitor unit 16 monitors the COM voltage Vcom, which is a voltage generated at the connection terminal com, and determines whether the COM voltage Vcom has deviated from a predetermined voltage range (for example, around 3.3 [V]). When determining that the COM voltage Vcom has deviated from the predetermined voltage range, the voltage monitoring unit 16 outputs the limit signal Ls to the VI conversion circuit 13. The voltage monitor 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 supplies the air-fuel ratio sensor 2 with the pump current converted not based on the voltage value input from the A / F detection circuit 11 but based on the voltage value whose upper and lower limits are limited by the limiting circuit 13a. Do. As a result, the pump current can be kept within a certain range of values without becoming excessively large or small. In other words, the limiting circuit 13a controls the input voltage to the A / F detection circuit 11 when the value of the voltage at the connection 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 the detailed configuration of the voltage monitor unit 16. The voltage monitor unit 16 includes two operational amplifiers OP4 and OP5.

  The operational amplifier OP4 has a non-inverted input terminal NI4 connected to the connection terminal com, an inverted input terminal II4 connected to the reference power supply Vref4, and an output terminal OUT4 connected to the VI conversion circuit 13.

  The reference power supply 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 the voltages. The output voltage is the limit signal Ls.

  In the operational amplifier OP5, the inverting input terminal II5 is connected to a connection point C to which the sense resistor Rs and the VI conversion circuit 13 are connected, the noninverting input terminal NI5 is connected to the reference power supply Vref5, and the output terminal OUT5 is a VI conversion circuit Connected to 13. The reference power supply Vref5 outputs, for example, 3.0 [V]. Therefore, 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 the voltages. The output voltage is the limit signal Ls.

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

  Thus, the pump current Ip can be kept within a certain range. Even if an over current occurs, the pump current Ip is kept within a certain range and does not become excessive or too small, so feedback control based on the pump current Ip can be quickly performed even after the over current occurrence has ended. Can be done. Further, since the pump current Ip can be contained in a predetermined range, it is possible to prevent the pump current Ip from being erroneously determined as abnormal after the end of the overcurrent.

  The voltage monitoring unit 16 may monitor not the voltage value of the connection terminal com shown in FIG. 6 but the voltage value of the connection point C where the sense resistor Rs and the constant voltage control unit 14 are connected. Since the voltage value of the COM terminal voltage Vcom can be monitored through the voltage drop at the sense resistor Rs, the occurrence of an overcurrent can be monitored at an appropriate point. In this case, the voltage monitoring unit 16 functions as a second detection unit that detects the voltage at the connection point C to which 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, for example, 7.0 [V] 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 an overcurrent or the like, the voltage input to the non-inverting input terminal NI4 is 3.3 [V]. Therefore, 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 the voltages. The output voltage is the limit signal Ls.

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

  As described above, the voltage monitoring unit 16 generates a limiting signal when the voltage at the connection point C rises and exceeds 7.0 [V], and similarly decreases and falls below 0.7 [V]. Output Ls 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 that it does not exceed or fall below the predetermined current value. For this reason, since the pump current Ip does not become excessive or excessively small, it is not erroneously determined that the air-fuel ratio sensor 2 and the control device 1 are abnormal. Moreover, since the period which transfers to a normal state can be shortened by feedback control after the end of an overcurrent, the erroneous abnormality detection by the abnormal value in a 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 stably controlled promptly based on the value of the pump current.

<3. Third embodiment>
Next, a third embodiment will be described. The third embodiment includes the same configuration as the first embodiment. Therefore, the differences from the first embodiment will be mainly described.

  If the pump current Ip is excessive with respect to the COM current Icom, the constant voltage control unit 14 can not absorb or replenish 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 at a constant voltage value (specified voltage value) than the ability of the VI conversion circuit 13 to apply the pump current Ip. In order to turn on the power, set the ability to conduct current 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 such that COM current Icom> pump current Ip. 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, the constant voltage control unit 14 can not control the connection terminal com to a constant voltage by supplying the pump terminal Ip having a capacity higher than the constant voltage control unit 14 can pass the current to the connection terminal com. To prevent. Therefore, the constant voltage control unit 14 can always conduct current absorption or replenishment for the pump current Ip supplied to the connection terminal com, and can hold the connection terminal com at a constant voltage.

<4. Modified example>
The present invention is not limited to the above embodiment. The invention is variable. Hereinafter, modified examples 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 of the limiting circuit 12 and the voltage monitoring unit 16. In this case, the VI conversion circuit 13 may include the limiting circuit 13a.

  Further, in the above embodiment, the limiting 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 functions described as software may be realized by hardware. Also, hardware or software may be realized by a combination of hardware and software.

1 air fuel ratio control device 2 air fuel ratio sensor 2a detection cell section 2b pump cell section 3 fuel injection device 4 fuel injection valve

Claims (5)

Exhaust gas of an internal combustion engine, comprising: a detection cell unit generating an air-fuel ratio voltage according to an air-fuel ratio; Control device for controlling an air-fuel ratio sensor provided in the
Output means for outputting an output voltage based on the air-fuel ratio voltage;
An energizing means for energizing a pump current to the pump cell portion so that the air fuel ratio becomes a predetermined ratio based on the output voltage;
Constant voltage means for controlling the voltage at the connection generated at the connection to a constant specified voltage value;
Limiting means for limiting the value of the pump current so as not to exceed the range of a predetermined current value;
Equipped with
The range of the predetermined current value, the constant voltage means the connection portion voltage, a control device according to claim ranges der Rukoto can be maintained within a predetermined range including the specified voltage value. In the control device according to claim 1,
The limiting means limits the value of the pump current not to exceed the range of the predetermined current value by limiting the value of the output voltage of the output means not to exceed the range of the predetermined voltage value. Control device. In the control device according to claim 1,
First detection means for detecting the connection voltage;
And further
The limiting means is configured such that the value of the output voltage of the energizing means is a predetermined voltage when the first detecting means detects that the connection voltage is higher or lower than the specified voltage value by a predetermined value or more. by limiting so as not to exceed the range of values, the control apparatus characterized by value of the pump current is limited so as not to exceed the range of the predetermined current value. In 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;
And further
When the second detecting means detects that the voltage at the connection point is higher or lower than a predetermined voltage value , the limiting means determines that the value of the output voltage of the energizing means has a predetermined voltage value range. by limiting so as not to exceed, the control apparatus characterized by value of the pump current is limited so as not to exceed the range of the predetermined current value. The control device according to any one of claims 1 to 4 .
Control means for controlling a fuel injection valve that injects fuel into the internal combustion engine;
Equipped with
The control means
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 injection amount of the fuel based on the air-fuel ratio;
A fuel injection device comprising:

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