JP7639632B2 - Heater current control device for A/F sensor - Google Patents

Description

The present invention relates to a device for detecting the state of gas contained in the exhaust gas of an internal combustion engine, and for passing electricity through the heaters of multiple A/F sensors equipped with activation heaters.

Conventionally, there is a device disclosed in, for example, Patent Document 1 that controls the energization of heaters in multiple air-fuel ratio (A/F: Air By Fuel) sensors with built-in heaters that are arranged in the exhaust path of an internal combustion engine. When the A/F sensor and its heater are in a low temperature state immediately after starting the vehicle, a large current is required to energize the heater in order to increase the temperature of the A/F sensor and activate it.

Therefore, in Patent Document 1, electricity is first supplied to the heater of the A/F sensor located upstream of the exhaust path, and then electricity is supplied to the heater of the A/F sensor located downstream. This limits the current flowing to the heater, and reduces the load on the battery and heater power supply system when the A/F sensor and its heater are in a low temperature state.

Japanese Patent Application Publication No. 8-232746

However, in the above conventional technology, the A/F sensor that delays the start of energization of the heater takes longer to reach its activation temperature, and starts detecting the air-fuel ratio later. As a result, the start of air-fuel ratio control of the internal combustion engine is delayed, causing a problem of increased emissions of harmful substances in the vehicle's exhaust gas.

In addition, since only exhaust gas from the internal combustion engine contributes to the heating of the heater during the delayed energization, it depends on the condition of the internal combustion engine, and the heating efficiency varies compared to heating the A/F sensor with a built-in heater. For example, when starting the engine in cold regions, the A/F sensor and its heater are low in temperature, and it takes time for the internal combustion engine to warm up and the exhaust gas temperature to rise, so it may take a long time for the sensor to reach its activation temperature.

The present invention was made in consideration of the above circumstances, and its purpose is to provide an A/F sensor heater current control device that can reduce the load on the power supply system when the A/F sensor is in a low temperature state while shortening the time it takes for multiple A/F sensors to reach their activation temperature.

According to the A/F sensor heater current control device of claim 1, when at least one of the temperatures of multiple A/F sensors equipped with activation heaters detected by multiple temperature detection units is below a predetermined value, the current control unit performs initial current control to control multiple current switches to activate two or more A/F sensors in parallel by currenting the multiple heaters one by one using a PWM signal .

With this configuration, when activating two or more A/F sensors in parallel during initial power control, power is applied to each of the heaters one at a time, reducing the load on the power supply system when the A/F sensors are in a low temperature state and shortening the time it takes for the A/F sensors to reach their activation temperature.

According to the heater current control device for an A/F sensor described in claim 1 , when the temperature of the A/F sensor targeted for activation exceeds a predetermined value, the current control section performs normal current control in which current is applied to two or more of the heaters in a superimposed manner. That is, when the current control section confirms that the temperature of the targeted A/F sensor exceeds a predetermined value, the control section shifts from initial current control to normal current control. Therefore, when the load on the power supply system is reduced, the control section can shift to normal current control.

According to the heater current control device of the A/F sensor of the present invention , the current control unit also transitions to normal current control when the current flowing through the heater falls below a predetermined value, thereby making it possible to transition to normal current control at the point when the load on the power supply system is more reliably reduced.

FIG. 1 is a functional block diagram illustrating a configuration of a heater current control device according to a first embodiment. Flowchart showing control contents FIG. 13 is a diagram showing PWM signals for driving two energization switches and energization currents to a heater when transitioning from initial energization control to normal energization control; FIG. 3 in the prior art A flowchart showing a process for calculating a duty ratio of a PWM signal in normal energization control. FIG. 11 is a diagram showing the PWM signals for driving two energization switches and the energization current to the heater when transitioning from the initial energization control to the normal energization control according to the second embodiment. FIG. 13 is a functional block diagram showing the configuration of a heater current control device according to a third embodiment. Flowchart showing control contents

First Embodiment
As shown in Fig. 1, A/F sensors 1(1) and 1(2) of this embodiment detect exhaust gas discharged from an internal combustion engine for a vehicle (not shown) and identify the state of gas contained in the exhaust gas, for example, the air-fuel ratio in the exhaust. The A/F sensor 1 is disposed in the exhaust passage of the internal combustion engine. The peripheral configurations of the A/F sensors 1(1) and 1(2) are symmetrical, so that in the following description, the reference numerals (1) and (2) will not be added unless there is a need to distinguish between them.

The A/F sensor 1 includes a sensor element 3 and a heater 4 for heating and activating the sensor element 3. The heater 4 is powered by a heater power supply system 5. The heater power supply system 5 supplies power from a power source 6 to the heater 4 via a wire harness 7 and a fuse 8. The power supply is controlled by a heater current control device 11.

The heater current control device 11 includes a microcomputer 12 and a heater drive control IC 13. The low-potential terminal of the heater 4 is connected to ground inside the heater current control device 11 via a current switch 14, such as an N-channel MOSFET, and a resistor element 15.

Both ends of the resistive element 15 are connected to the input terminals of an amplifier 16 built into the heater drive control IC 13, and the output signal of the amplifier 16 is input to the microcontroller 12 via a communication line 17 that connects the control IC 13 and the microcontroller 12.

Both ends of the sensor element 3 of the A/F sensor 1 are connected to input terminals of a temperature detection unit 18 of the heater drive control IC 13. The temperature detection unit 18 detects the temperature of the sensor element 3 based on a change in impedance of the sensor element 3 obtained by applying a voltage to the sensor element 3. The output signal of the temperature detection unit 18 is input to the microcomputer 12 via the communication line 17. The microcomputer 12, which corresponds to the current control unit, outputs a drive signal as a PWM (Pulse Width Modulation) signal to the gate of the current switch 14 via the heater drive control IC 13.

Next, the operation of this embodiment will be described. As shown in FIG. 2, when the microcomputer 12 detects the temperatures of the A/F sensors 1(1) and 1(2) via the heater drive control IC 13 (S1), it determines whether the temperature of either A/F sensor 1 is equal to or lower than a predetermined value (S2). Here, the degree to which the "predetermined value" is set depends on the power supply capacity of the heater power supply system 5 and the characteristics of the heater 4, but is set to, for example, about 25°C, which is considered to be room temperature.

If the temperature is equal to or lower than a predetermined value (S2; YES), alternating current control is performed as the initial current control (S4). As shown on the left side of FIG. 3, alternating current control is a control in which the PWM signals output to the gates of the current switches 14(1) and 14(2) are opposite in phase with a duty ratio of 50%, so that the heaters 4(1) and 4(2) are alternately energized.

During the alternating current control, the microcomputer 12 detects the current flowing through the heaters 4(1) and 4(2) via the heater drive control IC 13 (S5). It then determines whether the sum of the two current values is equal to or less than a predetermined value (S6). If the sum of the current values exceeds the predetermined value (NO), the process returns to step S4, and if it is equal to or less than the predetermined value (YES), the process moves to normal current control (S3). As shown on the right side of FIG. 3, normal current control is a control in which the duty ratio of the PWM signal output to the gates of the current switches 14(1) and 14(2) is set arbitrarily to less than 100% to energize the heaters 4(1) and 4(2).

In other words, with alternating current control, only one of heaters 4(1) and 4(2) is energized, and there is no period during which both are energized simultaneously. In this way, by alternately energizing heaters 4(1) and 4(2), A/F sensors 1(1) and 1(2) are heated alternately, and these are activated in parallel. On the other hand, with normal current control, there is a period during which both are energized simultaneously. Note that if the temperatures of both A/F sensors 1 exceed the predetermined value (S2; NO), the process also proceeds to step S2.

In the conventional technology shown in FIG. 4, when the power supply control for activating A/F sensors 1(1) and 1(2) starts, power is supplied to both heaters 4(1) and 4(2) in a superimposed manner, resulting in a high peak value of the sum of the currents. In contrast, when the initial power supply control of the present embodiment shown in FIG. 3 starts, power is supplied alternately to heaters 4(1) and 4(2), resulting in a lower peak value of the sum of the currents.

In normal energization control, as shown in FIG. 5, when the microcomputer 12 starts calculating the duty ratio (S11), it detects the temperature of the A/F sensor 1(1) and the energization current of the heater 4(1) (S12), and calculates the duty ratio of the PWM signal to be output to the gate of the energization switch 14(1) based on these (S13).

Then, similarly, the microcomputer 12 detects the temperature of the A/F sensor 1 (2) and the current flowing through the heater 4 (2) (S14), and calculates the duty ratio of the PWM signal to be output to the gate of the current flow switch 14 (2) based on these (S15). When the calculation of the duty ratio is completed (S16), the microcomputer 12 waits until the next calculation cycle is reached, that is, until the carrier cycle of the PWM control has elapsed (S17). If the current flow control to the heater 4 is still continuing at that point (S18; YES), the microcomputer 12 returns to step S11.

As described above, according to this embodiment, in the heater current control device 11, if at least one of the temperatures of the A/F sensors 1(1) and 1(2) detected by the temperature detection units 18(1) and 18(2) is equal to or lower than a predetermined value, the microcomputer 12 performs initial current control to control the current switches 14(1) and 14(2) so as to activate the A/F sensors 1(1) and 1(2) in parallel by energizing the heaters 4(1) and 4(2) one by one.

With this configuration, when activating A/F sensors 1(1) and 1(2) in parallel during initial power control, power is applied to heaters 4(1) and 4(2) one at a time, reducing the load on power supply system 5 when A/F sensor 1 is in a low temperature state and shortening the time it takes for the two A/F sensors 1 to reach their activation temperature.

When the temperature of the A/F sensor 1 targeted for activation exceeds a predetermined value or the current flowing through the heater 4 falls below a predetermined value, the microcomputer 12 performs normal current control to superimpose current on the heaters 4(1) and 4(2). That is, when the microcomputer 12 confirms via the current detection unit 16 that the current flowing through the power supply system 5 to the heater 4 falls below a predetermined value, it transitions from initial current control to normal current control. Therefore, when the load on the power supply system 5 is reduced, it is possible to transition to normal current control.

The microcomputer 12 also controls the energization switch 14 with a PWM signal, and when performing initial energization control, outputs PWM signals that are in opposite phase to each other, with a maximum duty ratio of 50%. Then, in normal energization control, the duty ratio of the PWM signal is calculated individually for each constant control period based on the temperature or the current, and set to an arbitrary value. As a result, in initial energization control, alternating energization control can be performed by easily setting the duty ratio, and in normal energization control, the duty ratio of the PWM signal can be appropriately set based on the temperature or current.

Second Embodiment
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals and the description thereof will be omitted, and the different parts will be described. In the second embodiment shown in FIG. 6, the setting of each duty ratio in the initial energization control is different from that in the first embodiment. In the first embodiment, the duty ratios of the two PWM signals are set to be equal to 50%, but in the second embodiment, one duty ratio is set to be greater than 50% and the other duty ratio is set to be less than 50%. The sum of the two duty ratios is set to 100%. By controlling in this way, it is possible to preferentially activate the A/F sensor that needs to be activated earlier.

Third Embodiment
A heater energization control device 21 of the third embodiment shown in Fig. 7 includes a microcomputer 22 and an A/F sensor detection IC 23 that replaces the heater drive control IC 13. The A/F sensor detection IC 23 includes only a temperature detection unit 18, and an output port of the microcomputer 22 is directly connected to the gate of the energization switch 14. In other words, the microcomputer 22 directly drives the gate of the energization switch 14 without going through a drive IC.

The drains of the energizing switches 14(1) and 14(2) are both connected to the upper end of a common resistor element 15. In other words, the microcomputer 23 detects the current flowing through the heaters 4(1) and 4(2) using one resistor element 15 and amplifier 16.

Next, the operation of the third embodiment will be described. As shown in FIG. 8, in the third embodiment, steps S7 and S8 are executed instead of steps S5 and S6 in the first embodiment. That is, when step S4 is executed, the temperature of the heater 4 is detected by the temperature detection unit 18 (S7). Then, it is determined whether or not both of the temperatures of the two heaters 4 exceed a predetermined value (S8), and if both exceed the predetermined value (YES), the process proceeds to step S3.

In the above process, the current flowing through the heater 4 detected by the resistance element 15 and the amplifier 16 is not used. However, the detected current is used, for example, in a process for monitoring the deterioration state of the A/F sensor 1.
As described above, the heater energization control device 21 of the third embodiment can be configured on a smaller scale than the heater energization control device 11 of the first embodiment.

Other Embodiments
The number of A/F sensors may be three or more.
The configuration of the third embodiment may be applied to the control of the first embodiment.
The energizing switch is not limited to a MOSFET, but may be a power transistor, an IGBT, or the like.
Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure.

In the drawing, 1 is an A/F sensor, 3 is a sensor, 4 is a heater, 5 is a heater power supply system, 11 is a heater power control device, 12 is a microcomputer, 13 is a heater drive control IC, 14 is a power switch, 15 is a resistive element, 16 is an amplifier, and 18 is a temperature detection unit.

Claims (6)

The device detects the state of gas contained in exhaust gas from an internal combustion engine, and energizes a plurality of A/F (Air By Fuel) sensors (1(1), 1(2)) each having an activation heater (4(1), 4(2)),
A plurality of temperature detection units (18(1), 18(2)) for detecting temperatures of the plurality of A/F sensors;
a plurality of energizing switches (14(1), 14(2)) respectively disposed in paths for energizing the plurality of heaters;
an energization control unit (12, 22) that controls the on/off of each of the plurality of energization switches;
a current detection unit (15, 16) for detecting a current passed through the heater,
The energization control unit controls the energization switches by a PWM (Pulse Width Modulation) signal,
when at least one of the plurality of temperatures detected by the plurality of temperature detection units is equal to or lower than a predetermined value, an initial energization control is performed in which the plurality of energization switches are controlled so as to activate two or more A/F sensors in parallel by energizing the plurality of heaters one by one using the PWM signal;
When the temperature of the A/F sensor to be activated exceeds the predetermined value, the control is switched to a normal energization control in which two or more of the plurality of heaters are energized in a superimposed manner;
The heater current control device for an A/F sensor also transitions to the normal current control when the current falls below a predetermined value. 2. The heater current control device for an A/F sensor according to claim 1 , wherein the current control unit calculates a duty ratio of the PWM signal based on at least one of the temperature and the current during the normal current control . 3. The heater current control device for an A/F sensor according to claim 2 , wherein the current control unit calculates the duty ratio individually for each constant control period. 4. The heater current control device for an A/F sensor according to claim 2 , wherein the current control unit sets the duty ratios of the plurality of PWM signals to arbitrary values when performing the normal current control. The number of the A/F sensors is "2",
4. The heater current control device for an A/F ratio sensor according to claim 2 , wherein the current control unit outputs PWM signals having mutually opposite phases with the maximum value of the duty ratio set to 50 % when performing the initial current control. The number of the A/F sensors is "2",
4. The heater current control device for an A/F sensor according to claim 2 or 3, wherein the current control unit, when performing the initial current control, sets the sum of the duty ratios of the two PWM signals to be 100 % or less, and inverts one PWM signal to generate the other PWM signal.

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