JP2572405B2 - Control device for heater provided in oxygen concentration sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling electric power supplied to a heater provided in an oxygen concentration sensor for detecting an oxygen concentration in exhaust gas of an internal combustion engine.

[Conventional technology]

As a control device of the heater of the above-mentioned oxygen concentration sensor,
As shown in Japanese Patent Application Laid-Open No. 60-125553, an exhaust temperature is predicted from an intake air amount, a fuel injection amount, a cooling water temperature, an engine speed, etc., and the predicted exhaust temperature and the target temperature of the oxygen concentration sensor are detected. And a configuration in which the target power to be supplied to the heater is determined according to the comparison result.
As disclosed in Japanese Patent Application Laid-Open No. 60-214251, a configuration in which a basic power amount is set from an intake pipe pressure and an engine speed and a target power is determined by correcting the basic power amount in accordance with the intake air temperature. It is known.

[Problems to be solved by the invention]

By the way, when a vehicle equipped with an internal combustion engine having the above-described device performs start acceleration after idling due to a signal stop or the like, that is, when the operation of the engine shifts from the idle state to the load operation state, While the target power supplied to the heater decreases in accordance with the state change, the exhaust temperature rises later than the change in the operating state of the engine, so the rise in the exhaust temperature is delayed immediately after the transition to the load operation. During this time, the temperature of the detection element of the oxygen concentration sensor may decrease, and the temperature of the detection element may fall below the activation temperature.

Therefore, in order to solve such a problem, it is conceivable to correct the target power determined by the operation state immediately after the shift to the load operation, but when the increase correction is performed with a fixed correction amount, Since the exhaust gas temperature changes greatly depending on the warm-up state of the engine, the intake air temperature state, etc., the target power for the heater becomes too large, and the heater temperature exceeds the limit temperature, which may cause deterioration of elements constituting the heater. As a result, the detection element cannot be maintained at the activation temperature. Also, when the correction amount is determined according to the warm-up state of the engine or the intake air temperature state, the correction amount becomes extremely different, so that the calculation of the correction amount becomes complicated and the configuration becomes complicated. I will.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a heater control device provided in an oxygen concentration sensor capable of realizing a decrease in the temperature of a detection element of the oxygen concentration sensor immediately after a transition from idle to load operation with a simple configuration. .

[Means for solving the problem]

In order to solve the above problems, in the present invention, as shown in FIG. 9, a detecting element for detecting the oxygen concentration in the exhaust gas of the internal combustion engine,
An oxygen concentration sensor installed in an exhaust system of an internal combustion engine having a heater for heating the detecting element; operating state detecting means for detecting an operating state of the engine; and an operating state detected by the operating state detecting means Target power setting means for setting target power to be supplied to the heater in accordance with the following: control means for controlling power to be supplied to the heater in accordance with the target power set by the target power setting means; Idle detection means for detecting a state, state change detection means for detecting that the engine has shifted from an idle state to a non-idle state based on the detection result of the idle detection means, and state change detected by the state change detection means In this case, a lower limit value for the target power set by the target power setting means is set for a predetermined time from the time when the state change occurs, and the target power is set to the lower limit. It is characterized by having a limiting means for limiting the value.

[Action]

According to the above configuration, when the state change detection unit detects that the engine has transitioned from idle to non-idle,
A predetermined time from that point in time by the limiting means, a lower limit value is set for the target power set by the target power setting means,
Since the target power is limited by the lower limit, the power supplied to the heater for a predetermined time is set to a value equal to or higher than the lower limit.

〔Example〕

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

First, FIG. 1 shows a vehicle internal combustion engine (hereinafter, referred to as a vehicle) equipped with a heater control device provided in an oxygen concentration sensor of the present embodiment.
Abbreviated as engine. FIG. 1 is a schematic system diagram showing peripheral devices.

In the figure, 1 is an engine, 2 is a piston, 3 is a cylinder, 4 is a cylinder head, an exhaust manifold 6 is provided at an exhaust port 5 of each cylinder of the cylinder head 4, and an intake port 7 is provided at an intake port 7 of each cylinder of the cylinder head 4. The intake manifolds 8 are respectively connected. The intake manifold 8 is connected to a surge tank 9 for preventing pulsation of intake air, and the surge tank 9 is provided with an intake pressure sensor 10 for detecting a pressure in the intake manifold 8, that is, an intake pipe pressure Pm. ing.

Next, 11 is a throttle valve that controls the amount of intake air sent to each cylinder via the surge tank 9, 12 is a bypass passage for intake air that bypasses the throttle valve 11, and 13 is an intake air temperature sensor that detects intake air temperature. The throttle valve 11 is directly connected to a throttle position sensor 14 having a throttle valve opening sensor that outputs a signal corresponding to the opening of the throttle valve 11 and an idle switch that is turned on when the engine 1 is idling. ing. Reference numeral 15 denotes a known device mounted on the exhaust manifold 6 and provided with a detecting element for detecting the oxygen concentration in the exhaust gas and a heater made of platinum for heating, as disclosed in Japanese Patent Application Laid-Open No. 60-233342. An oxygen concentration sensor, 16 is a water temperature sensor for detecting a cooling water temperature of the engine 1, 17 is a distributor for applying a high voltage output from an igniter 19 at a predetermined timing to a spark plug 18 of the engine 1, and 20 is a distributor.
Reference numeral 17 denotes a rotation speed sensor attached to the engine 17 and generates a pulse signal corresponding to the rotation speed of the engine 1.

Various detection signals of the intake pressure sensor 10, the intake temperature sensor 13, the throttle position sensor 14, the oxygen concentration sensor 15, the water temperature sensor 16, and the rotation speed sensor 20 are input to a control circuit 25. On the basis of the fuel injection amount control of the fuel injection valve 26, the ignition timing control of the spark plug 18,
Alternatively, various control processes such as control of the heater of the oxygen concentration sensor 15 are executed.

Next, FIG. 2 is a block diagram showing the configuration of the control circuit 25 described above. In the figure, 31 is a detection element of the oxygen concentration sensor 15
An applied power supply for applying a predetermined voltage to 15a, 32 is a resistor for detecting a current flowing through the detection element 15a, and 33 is a resistor 3
An amplification circuit for amplifying the voltage drop in 2 by a predetermined factor, 34 is an output signal from the amplification circuit 33, that is, an analog signal corresponding to the oxygen concentration in the exhaust gas, the intake pressure sensor 10, the intake temperature sensor 13, the throttle position An A / D converter that receives an analog signal detected by the opening degree sensor 14a of the sensor 14, the water temperature sensor 16, and the like, and converts the signal into a digital signal. Reference numeral 35 denotes a microcomputer 37 composed of a CPU, ROM, RAM, etc., based on a signal input via the A / D converter 34 and a signal from the idle speed sensor 20 and the idle switch 14b of the throttle position sensor 14. A driving circuit controlled by the output control signal and outputs a driving signal to the fuel injection valve 26 to supply the engine 1 with a predetermined amount of fuel calculated by the microcomputer 37. is there. The igniter 19 is also controlled by the microcomputer 37 to output a high voltage to the distributor 17 at a predetermined timing.

Next, reference numeral 38 denotes an energization control circuit for controlling the power supplied to the heater 15b of the oxygen concentration sensor 15, which controls energization from the heater power supply 39 in accordance with a control signal of the microcomputer 37. A heater voltage detection circuit 40 detects a heater voltage when the heater 15b is energized, and a heater current detection circuit 41 similarly detects a heater current.

In the control circuit of this embodiment configured as described above, various controls such as fuel injection amount control, ignition timing control, and heater control of the oxygen concentration sensor are executed as described above. Regarding the heater control of the oxygen concentration sensor which is the main control process according to the present invention,
This will be described in detail according to the program shown in FIG. 6 and FIG.

The flowchart of the program shown in FIG.
sec.], and represents a process of calculating a duty ratio of heater energization for executing energization from the heater power supply 39 to the heater 15b in accordance with the operating state of the engine 1 and the detection result of the oxygen concentration sensor 15. I have.

When the process is started, first, in step 301, the engine speed N
e, intake pipe pressure Pm, intake temperature Ti, heater voltage Vh, heater current Ih, etc.
Move to 2.

In step 302, based on the heater voltage Vh and the heater current Ih read in step 301, the amount of power when the heater 15b is energized for a predetermined time, for example, 100 [m sec.], That is, the duty ratio 100 The process of calculating the% electric energy A is executed, and the process proceeds to step 303. Less than,
All the electric energy is the electric energy per 100 [m sec.].

Next, in step 303, the basic power amount B of the heater 15b is calculated from the map M1 or an arithmetic expression as shown in FIG. 4, for example, using the engine speed Ne and the intake pipe pressure Pm obtained in step 301 as parameters. , And the process proceeds to subsequent step 304. Here, in the map M1, the fourth
As is clear from the figure, the engine speed Ne and the intake pipe pressure Pm
The basic electric energy B when the intake air temperature Ti is 20 ° C. is set as a parameter. This is, of course, when the intake pipe pressure Pm is large or the engine speed Ne is large. The amount of fuel injection into 1 increases,
Since the temperature of the exhaust gas rises and the detecting element 15a can be heated by the exhaust gas, the electric power supplied to the heater 15b is reduced.
When Pm is small, the exhaust gas temperature decreases and the exhaust element cannot heat the detection element 15a, so that the power supplied to the heater 15b is set to be large.

Next, in step 304, a process of obtaining a correction power amount b with respect to the basic power amount B from the map M2 using the intake air temperature Ti obtained in step 301 as a parameter is executed.

Then, in step 305, a process of calculating the target power amount C to be actually supplied to the heater 15b is performed using the following equation C = B + b using the basic power amount B and the corrected power amount b as parameters.

Here, the map M2 used in step 304 is, for example, as shown in FIG.
Is set to a negative value when Ti> 20 [° C] centering around 20 ° C, and to a positive value when Ti <20 [° C]. Have been. This is because the map M1 was set under the condition of Ti = 20 [° C.] in the above description, and when Ti = 20 [° C.], the value of the map M1 can be used as it is. Set the correction power amount b to “0”, and when Ti> 20 [° C], set the map
If the value of M1 is used as it is, the oxygen concentration sensor 15 will be too hot, so a negative correction value is set.

Next, in step 306, it is determined whether the engine 1 is in a low-speed operation state, that is, in an idle operation state, based on a signal from the idle switch 14b of the throttle position sensor 14.
Proceed to 307.

Then, in step 307, the counter CIDL is counted up by "1". Next, at step 308, the counter CIDL is set to 1
Check whether the value is 00 or more, and if it is 100 or more, limit the counter CIDL to 100 in step 309, and then go to step 31
Proceed to 6.

If it is determined in step 306 that the vehicle is not in the idle operation state, the process proceeds to step 310, where the counter CIDL is counted down by "1". Next, in step 311, it is checked whether the counter CIDL is 0 or less. If the counter CIDL is 0 or less, CIDL is limited to 0, and the process proceeds to step 313. In step 313, it is determined whether or not the counter CIDL is greater than 10. If CIDL> 10, step 314 is executed.
If CIDL ≦ 10, the process proceeds to step 316. Step 314
Then, the target electric energy C obtained in step 305 is 20 [w].
It is determined whether or not the above is satisfied. If C ≧ 20, the process proceeds to step 316.
If C <20, the process proceeds to step 315. In step 315, the target power amount C is corrected to 20 [w], and thereafter, the process proceeds to step 316.

The target amount of power C determined in step 316 in the above processing blunted with previous target amount of power C _i-1 and obtaining the current target power amount C _i. This process prevents a sudden change in the temperature of the heater 15b.

When the current target electric energy C _i is obtained in this way,
In the following step 316, the target electric energy C _i and the above-described step 3
Duty for supplying current target power amount C _i to the heater 15b using the equation _{D = (C i / A)} × 100 where a duty ratio of 100% electric energy A is a parameter determined at 02 The ratio D is calculated, and the process ends.

The flowchart of the program shown in FIG. 6 is a control for turning on and off the energization control circuit 38 in accordance with the duty ratio D obtained by the program of FIG. 3 to control the energization to the heater 15b. A program, 1
It is executed every [m sec.].

When the process is started, first, in step 601, the counter C
It is determined whether 100 _ms is C _{100 ms} ≧ 100. If C _{100 ms} ≧ 100, C _{100 ms} is cleared to 0 in step 602 and the process proceeds to step 603. If C _{100 ms} <100, the process bypasses step 602 and step 603 Proceed to.

In step 603, the duty ratio D obtained in the above process is compared with the counter C _{100 ms} . If D ≧ C _{100 ms} , the process proceeds to step 604, where the energization control circuit 38 is turned on to energize the heater 15b. , D <C _100ms , step 6
Proceeding to 05, the power supply control circuit 38 is turned off to stop power supply to the heater 15b. Then, in step 606, _C100ms is counted up by "1", and then this processing is terminated.

FIG. 7 is a time chart showing a difference in operation and effect between the configuration of the present embodiment and the conventional configuration. Conventionally, when the vehicle starts from an idle state, immediately after the start, the driving state (intake pipe pressure Pm, rotation In response to the change in the number Ne), the amount of power supplied to the heater 15b decreases as shown by the dashed line, but the exhaust gas temperature at that time starts to rise with a large delay with respect to the change in the operating state. As the sensor temperature decreases, the sensor activation limit temperature (650 ° C)
However, in the case of the configuration of the present embodiment, the supplied electric energy (target electric energy C _i ) is lower than the lower limit 20 [w] for a predetermined time immediately after the vehicle starts moving.
Is guarded so as not to fall below the temperature, so that it is possible to prevent the sensor temperature from dropping below the sensor activation limit temperature.

Further, in the present embodiment, the time for setting the lower limit is determined according to the continuation time of the idle state. This is because if the idle state is short, the exhaust manifold 6 is still at a high temperature due to the effect of the load operation state before the idle state is left. This is because unnecessary power supply can be prevented by determining the time for setting the lower limit according to the duration of the idle installation state, and even if the lower limit is set, the temperature of the heater becomes lower. It is possible to sufficiently prevent the temperature from exceeding the limit temperature.

Further, in the present embodiment, a lower limit value is set for the target power amount to the heater 15b so that the target power amount does not become lower than the lower limit value.
It is possible to prevent the sensor temperature from dropping below the sensor activation limit temperature.

By the way, in consideration of the exhaust gas temperature, the basic electric energy B is determined so that the temperature of the detecting element 15a is kept at a constant value. Therefore, the basic electric energy B is set to a larger value as the exhaust gas temperature is lower. That is, it is possible to grasp the operation state based on the basic electric energy B. Therefore, as shown in FIG.
The step 306 in FIG. 3 may be controlled based on whether or not B ≧ 25.

Further, in the above-described embodiment, the engine speed Ne and the intake pipe pressure Pm are used when obtaining the basic electric energy B. In addition, the intake air amount and the opening degree of the throttle valve 11 are used. Or simply the engine speed Ne
Or only one of the intake pipe pressure Pm and the like.

Further, in the above embodiment, the energization control of the heater 15b is set to 100
Although the control is executed by the duty control based on the energizing time per [m sec.], The power supply to the heater 15b may be obtained, for example, and the voltage applied to the heater 15b may be controlled.

〔The invention's effect〕

As described above, according to the present invention, when the state change detecting means detects that the engine has shifted from idle to non-idle, the limiting means sets the target power for a predetermined time from the target power setting means. Since a lower limit value is set for the target power and the target power is limited by the lower limit value, the power supplied to the heater for a predetermined time is set to a value equal to or higher than the lower limit value. , And the lower limit is only applied, so that there is an excellent effect that prevention of a decrease in the temperature of the detection element can be realized with a simple configuration.

[Brief description of the drawings]

1 is a schematic system diagram showing an engine equipped with a control device for a heater for an oxygen concentration sensor according to an embodiment of the present invention and peripheral devices thereof, FIG. 2 is a block diagram showing a configuration of a control circuit 25, and FIG. Is a flowchart showing a program for calculating a duty ratio in heater control of the oxygen concentration sensor executed by the control circuit 25, FIG. 4 is a graph showing a map M1 for obtaining a basic electric energy B, and FIG. Quantity b
FIG. 6 is a flowchart showing an energization processing program for energizing the heater in accordance with the duty ratio obtained in the processing of the program of FIG. 3, and FIG. FIG. 8 is a part of a flowchart showing another embodiment of the present invention, and FIG. 9 is a schematic diagram of the present invention. FIG. 1 ... engine, 6 ... exhaust manifold, 10 ... intake pressure sensor, 13 ... intake temperature sensor, 14 ... throttle position sensor, 14 b ... idle switch, 15 ... oxygen concentration sensor, 20 ... rotational speed Sensor, 25 Control circuit, 37 Microcomputer, 38 Energization control circuit.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-56-130650 (JP, A) JP-A-58-82149 (JP, A)

Claims (1)

(57) [Claims] An oxygen concentration sensor installed in an exhaust system of an internal combustion engine including a detection element for detecting an oxygen concentration in exhaust gas of an internal combustion engine, a heater for heating the detection element, and an operation state of the engine. Operating state detecting means for detecting, target power setting means for setting target power to be supplied to the heater according to the operating state detected by the operating state detecting means, and a target set by the target power setting means Control means for controlling electric power supplied to the heater in accordance with electric power; idle detection means for detecting an idle state of the engine; and an engine having shifted from an idle state to a non-idle state based on a detection result of the idle detection means. State change detecting means for detecting that the state change is detected by the target power setting means for a predetermined time from the time when the state change occurs. To set the lower limit for the target power to be constant, the control unit of the heater provided in the oxygen concentration sensor, characterized in that it comprises a limiting means for limiting the target electric power in the lower limit.