Heater control device for gas sensor

Abstract

To provide a heater control device for a gas sensor such that a standby time of electrification for a heater of a gas sensor can be properly set.SOLUTION: There is provided a heater control device for a gas sensor that controls a heater which heats a sensor element of a gas sensor provided upstream from a sub-muffler of an exhaust pipe of an engine mounted on a vehicle. The heater control device for the gas sensor comprises: a front tilt angle acquisition part which acquires a front tilt angle as a tilt angle of the vehicle in a front tilt state; a backflow determination part which determines whether or not condensate water flows backward from the sub-muffler to an upstream side based upon the front tilt angle; an exhaust atmospheric pressure rise amount acquisition part which acquires an amount of rise in exhaust pressure as the pressure in the exhaust pipe when the backflow determination part makes an affirmative determination; and a standby time setting part which sets a standby time from a next start of the engine to a start of electrification of the heater longer as the amount of rise is larger.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a heater control device for a gas sensor.

Background Art

[0002] A gas sensor provided in an exhaust pipe of an engine mounted on a vehicle is provided with a heater for heating a sensor element of the gas sensor. After the sensor element reaches the activation temperature by the heater, predetermined engine control is executed based on the detection value of the sensor element. Condensed water may remain in the exhaust pipe. For example, when the gas sensor heated to a high temperature by the heater is wetted by the condensed water in the exhaust pipe at the start of the engine, the gas sensor may be damaged. Therefore, a standby time for waiting for energization of the heater is set until the condensed water is discharged from the exhaust pipe or evaporated after the engine is started. For example, in Patent Document 1, it is considered that the larger the forward tilt angle of the vehicle, the larger the residual amount of condensed water that is not discharged from the exhaust pipe, and the above standby time is set for a long period.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the forward tilt angle of the vehicle is not a value that directly correlates with the residual amount of condensed water in the exhaust pipe. For example, the residual amount of condensed water in the exhaust pipe is also affected by the outside air temperature and the like. Therefore, there is a possibility that the standby time is set off with respect to the elimination time required for the condensed water to be discharged or evaporated from the exhaust pipe. For example, if the standby time is set short with respect to the elimination time, there is a possibility that the power supply to the heater is started with condensed water remaining in the exhaust pipe. As a result, there is a possibility that the high-temperature gas sensor is damaged by being wetted with water. Further, if the standby time is set long with respect to the elimination time, there is a possibility that the power supply to the heater is still waiting even after the condensed water is discharged from the exhaust pipe. As a result, there is a possibility that the start of engine control based on the detection value of the sensor element is delayed.

[0005] Therefore, an object of the present invention is to provide a heater control device for a gas sensor that can appropriately set the standby time for energizing the heater of the gas sensor.

Means for Solving the Problems

[0006] The above object is a heater control device for a gas sensor that controls a heater for heating a sensor element of a gas sensor provided upstream of a sub-muffler of an exhaust pipe of an engine mounted on a vehicle, the forward tilt angle acquisition unit for acquiring the forward tilt angle which is the tilt angle when the vehicle tilts forward, a backflow determination unit that determines whether or not backflow of condensed water from the sub-muffler to the upstream side has occurred based on the forward tilt angle, an exhaust pressure increase amount acquisition unit that acquires an increase amount of the exhaust pressure which is the pressure in the exhaust pipe when an affirmative determination is made by the backflow determination unit, and a standby time setting unit that sets a longer standby time from the start of the next engine start until the power supply to the heater is started as the increase amount is larger. It can be achieved by a heater control device for a gas sensor provided with.

Effects of the Invention

[0007] According to the present invention, it is possible to provide a heater control device for a gas sensor that can appropriately set the standby time for energizing the heater of the gas sensor.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0009] [Schematic Configuration of Vehicle] Figure 1A is a schematic configuration diagram of the vehicle 1. An engine 10, which is a driving power source, is provided in the vehicle body 2 of this vehicle 1. Therefore, the vehicle 1 is an engine vehicle, but it may also be a hybrid vehicle equipped with a motor in addition to the engine 10 as a driving power source. The engine 10 includes an engine body 12 and an exhaust pipe 14. The engine body 12 is provided with a plurality of cylinders. The exhaust pipe 14 is connected to the exhaust ports of the respective cylinders of the engine body 12. Exhaust from each cylinder of the engine body 12 flows through the exhaust pipe 14. The engine body 12 is provided in the front of the vehicle body 2. The exhaust pipe 14 extends rearward from the engine body 12 in the vehicle body 2. A sub-muffler 16 that forms a part of the exhaust pipe 14 is provided in the exhaust pipe 14. Note that a main muffler (not shown) is provided on the downstream side of the sub-muffler 16 of the exhaust pipe 14.

[0010] An exhaust gas sensor 20, which will be described in detail later, is provided on the upstream side of the sub-muffler 16 of the exhaust pipe 14. The gas sensor 20 is an air-fuel ratio sensor that detects the air-fuel ratio of the exhaust gas, but is not limited thereto, and may be an oxygen concentration sensor that detects the oxygen concentration in the exhaust gas.

[0011] Vehicle 1 is equipped with an ECU (Electronic Control Unit) 50. The ECU 50 is mainly composed of a computer including volatile and non-volatile memories such as a CPU (Central Processing Unit), a RAM (Random Access Memory), and a ROM (Read Only Memory). The ECU 50 realizes various control processes related to the engine 10 by executing programs installed in the memory on the CPU. The ECU 50 is an example of a gas sensor heater control device, and specifically, functionally realizes a forward tilt angle acquisition unit, a reverse flow determination unit, an exhaust pressure increase amount acquisition unit, and a standby time setting unit, which will be described in detail later.

[0012] The ECU 50 calculates the air-fuel ratio of the exhaust based on the output value of the gas sensor 20. Based on the calculated air-fuel ratio, the ECU 50 performs feedback control on the intake air amount and fuel injection amount of the engine 10 so that the air-fuel ratio of the exhaust of the engine 10 becomes the target air-fuel ratio.

[0013] A sensor group 60 composed of a plurality of sensors is connected to the ECU 50. The sensor group 60 includes an air flow meter that detects the intake air amount, a crank angle sensor that detects the rotational speed of the engine 10, and a vehicle tilt sensor that detects the tilt angle of the vehicle 1 in the front-rear direction with respect to the horizontal direction.

[0014] The gas sensor 20 includes a sensor element 21 and a heater 22. The sensor element 21 outputs an output current value corresponding to the air-fuel ratio of the exhaust to the ECU 50. The ECU 50 acquires the output current value of the sensor element 21 and calculates the air-fuel ratio based on this output current value. The heater 22 activates the sensor element 21 by heating it to maintain the sensor element 21 at the activation temperature. The ECU 50 executes heater energization control for controlling the energization current to the heater 22. The ECU 50 controls the temperature of the sensor element 21 by executing the heater energization control. The above-described feedback control is executed based on the detection value of the sensor element 21 in a state where the sensor element 21 is maintained at the activation temperature.

[0015] Here, the inner diameter of the sub-muffler 16 is larger than that of the exhaust pipe 14. Therefore, condensed water W may be stored in the sub-muffler 16. FIG. 1B is a diagram showing the state of the condensed water W in the sub-muffler 16 when the vehicle 1 is horizontal. FIG. 1C is a diagram showing the state of the condensed water W in the sub-muffler 16 when the vehicle 1 is tilted forward. As shown in FIG. 1B, when the vehicle 1 is horizontal, condensed water W is stored in the sub-muffler 16. When the vehicle 1 is in a forward-tilted posture as shown in FIG. 1C, the condensed water W in the sub-muffler 16 flows backward to the upstream side of the sub-muffler 16. For example, if the heater 22 of the gas sensor 20 is energized immediately after the engine 10 is started with the condensed water W remaining in the exhaust pipe 14 upstream of the sub-muffler 16, the high-temperature gas sensor 20 may be wetted by the condensed water W lifted by the exhaust. Therefore, the ECU 50 executes standby time setting control for setting the standby time from the start of the engine 10 until the energization of the heater 22 is started.

[0016] [Standby time setting control] FIG. 2A is a flowchart illustrating the standby time setting control executed by the ECU 50. This control is repeatedly executed in the ignition-on state. The ECU 50 acquires the forward tilt angle of the vehicle 1 (step S1). Step S1 is an example of the process executed by the forward tilt angle acquisition unit.

[0017] Next, the ECU 50 determines whether or not condensed water flows backward from the sub-muffler 16 to the upstream side based on the forward tilt angle (step S2). Specifically, when the forward tilt angle is equal to or greater than the determination value A, it is determined that the condensed water flows backward. The determination value A is the forward tilt angle at which the condensed water W starts to flow backward from the sub-muffler 16 in a full-water state. If the result in step S2 is No, this control ends. Step S2 is an example of the process executed by the backward flow determination unit.

[0018] If the answer is Yes in step S2, the ECU 50 acquires the amount of increase in the exhaust pressure since the determination of Yes in step S2 (step S3). The amount of increase in the exhaust pressure is a value correlated with the residual amount of the condensed water W remaining in the exhaust pipe 14 by flowing backward upstream from the sub-muffler 16. This is because the larger the residual amount of the condensed water W in the exhaust pipe 14, the smaller the effective cross-sectional area in the exhaust pipe 14 and the higher the exhaust pressure. The amount of increase in the exhaust pressure may be calculated by an arithmetic expression. For example, the amount of increase in the exhaust pressure may be calculated based on the volumetric efficiency. The volumetric efficiency can be calculated, for example, by the following arithmetic expression. Volumetric efficiency = Volume flow rate of intake air per cycle per cylinder / (Exhaust volume per cylinder × 100%) Also, the amount of increase in the exhaust pressure may be calculated based on the decrease amount of the intake air amount, or may be calculated based on the detected value of a pressure sensor that detects the pressure in the exhaust pipe 14. Step S3 is an example of the process executed by the exhaust pressure increase amount acquisition unit.

[0019] Next, the ECU 50 determines whether or not the amount of increase in the exhaust pressure is equal to or greater than the threshold value B (step S4). The threshold value B is set in consideration of minute fluctuations in the exhaust pressure due to factors other than the condensed water W remaining in the exhaust pipe 14. Minute fluctuations in the exhaust pressure due to factors other than the condensed water W are caused, for example, by a deviation in the exhaust timing from each cylinder of the engine body 12. The threshold value B is set to exclude minute fluctuations in the exhaust pressure caused by such factors and set the standby time. Therefore, the threshold value B is set to the amount of fluctuation in the exhaust pressure that can be caused by a deviation in the exhaust timing. Thus, if the answer is No in step S4, this control ends.

[0020] If the answer is Yes in step S4, the ECU 50 refers to the map shown in FIG. 2B and sets the waiting time from the next start of the engine 10 until the energization of the heater 22 is started based on the increase amount of the exhaust pressure (step S5). FIG. 2B is a map that defines the relationship between the increase amount of the exhaust pressure and the waiting time. When the increase amount of the exhaust pressure is equal to or greater than the threshold value B, the greater the increase amount of the exhaust pressure, the longer the waiting time is defined. As described above, the greater the increase amount of the exhaust pressure, the greater the residual amount of the condensed water W in the exhaust pipe 14 upstream of the sub-muffler 16 is considered to be. Also, the greater the residual amount of the condensed water W, the longer the removal time required for the condensed water W to be discharged from the exhaust pipe 14 or evaporated from the start of the engine 10 becomes. Step S5 is an example of the process executed by the waiting time setting unit.

[0021] [Heater energization control] FIG. 3 is a timing chart illustrating the heater energization control executed by the ECU 50. FIG. 3 shows the transitions of the engine speed, the inclination angle of the vehicle 1, the exhaust pressure, and the energization current of the heater 22. The energization current of the heater 22 in the state where the engine 10 is driven is maintained substantially constant so that the sensor element 21 is maintained at the activation temperature (time t0). When the forward inclination angle of the vehicle 1 becomes equal to or greater than the determination value A (time t1), the condensed water W flows backward from the sub-muffler 16 and the exhaust pressure begins to rise (time t2). After that, when the forward inclination angle becomes less than the determination value A, the backward flow of the condensed water W stops and the condensed water W is returned to the sub-muffler 16 by the exhaust and the exhaust pressure begins to decrease (time t3). After that, the engine 10 stops and the energization current to the heater 22 becomes zero (time t4). Since the increase amount of the exhaust pressure from this time t2 to immediately before the stop of the engine 10 at time t4 is equal to or greater than the threshold value B, the waiting time is set based on the map of FIG. 2B.

[0022] Next, the engine 10 starts, but the energization current to the heater 22 is maintained at zero before the elapse of the above-described waiting time (time t5). When the set waiting time elapses from the start of the engine 10, the condensed water W is considered to have been discharged or evaporated downstream of the gas sensor 20, and the energization of the heater 22 is started (time t6).

[0023] As described above, the waiting time is set based on the amount of increase in the exhaust pressure correlated with the residual amount of the condensed water W in the exhaust pipe 14. Therefore, the waiting time is appropriately set corresponding to the evacuation time required for the condensed water W to be discharged or evaporated to the downstream side of the gas sensor 20 after the engine 10 is started. Thereby, water ingress into the high-temperature gas sensor 20 due to the waiting time being set short with respect to the evacuation time is suppressed. Further, a delay in the start of engine control based on the detection value of the sensor element 21 due to the waiting time being set long with respect to the evacuation time is suppressed.

[0024] Note that the amount of increase in the exhaust pressure at the start of the engine 10 may be the amount of increase from the exhaust pressure at the time when it is determined Yes in step S2 until the exhaust pressure becomes maximum. This is because the condensed water W that has flowed backward may not return to the sub-muffler 16.

[0025] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Explanation of Reference Numerals

[0026] 10 Engine 12 Engine body 14 Exhaust pipe 16 Sub-muffler 20 Gas sensor 21 Sensor element 22 Heater 50 ECU (Gas sensor heater control device, forward tilt angle acquisition unit, backflow determination unit, exhaust pressure increase amount acquisition unit, waiting time setting unit) W Condensed water

Claims

[Claim 1] A heater control device for a gas sensor that controls a heater for heating a sensor element of a gas sensor provided upstream of a sub-muffler in an exhaust pipe of an engine mounted on a vehicle, a forward tilt angle acquisition unit that acquires a forward tilt angle that is a tilt angle when the vehicle is tilted forward; a backflow determination unit that determines whether or not a backflow of condensed water from the sub-muffler to an upstream side has occurred based on the forward tilt angle; and an exhaust pressure increase amount acquisition unit that acquires an increase amount of an exhaust pressure, which is a pressure in the exhaust pipe, when a positive determination is made by the backflow determination unit; a standby time setting unit that sets a standby time from the next start of the engine until the start of current supply to the heater to a longer time as the amount of increase increases.

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