JP3606273B2 - Energization control device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an energization control device having a function of performing A / D conversion of a load current or a load voltage during an on period of an energization pulse to a load while performing duty control on energization to a load.
[0002]
[Prior art]
Conventionally, duty control, which is widely used for load energization control, repeatedly turns on / off energization of a load in a short cycle, and sets the ratio (duty ratio) of the on-time (width of energization pulse) per cycle. By controlling, load current and load voltage are controlled. For example, energization control of a heater that heats an element of an air-fuel ratio sensor installed in an exhaust pipe of an internal combustion engine is also performed by duty control, A / D conversion of the heater current and voltage is taken into a microcomputer, and the detected value Based on this, the heater power is feedback-controlled and heater abnormality diagnosis is performed.
[0003]
When duty control of the heater energization is performed, as shown in FIG. 6, the heater energization is determined on / off in a very short cycle T1, and an integer n times (T1 × n) of the determination cycle T1 is determined for duty control. Duty control is performed as one cycle. Accordingly, when the duty ratio is D%, the energization is turned on every T1 × n hours, and the energization is turned off when T1 × n × D / 100 has elapsed since that time. That is, an energization pulse having a pulse width of T1 × n × D / 100 is output to the heater every T1 × n hours. At this time, the A / D conversion circuit is activated at a constant cycle T2, but is not synchronized with the cycle of the duty control.
[0004]
When A / D conversion is performed, the energization pulse width (T1 ×) is longer than the total time T3 of the time until the input signal of the A / D converter is stabilized (A / D stabilization time) and the A / D conversion processing time. If n × D / 100) is short, A / D conversion cannot be performed accurately. Therefore, the A / D prohibition flag is set to “prohibited” during the period from when the energized pulse is turned on (rising timing) until the total time T3 elapses. And A / D conversion is prohibited. As a result, the period during which A / D conversion is possible is a period in which the energization pulse is on and the A / D prohibition flag is “permitted”.
[0005]
[Problems to be solved by the invention]
However, in the above prior art, since the duty control cycle (T1 × n) and the A / D conversion execution cycle T2 are not synchronized, the energization pulse width is the sum of the determination cycle T1 and the A / D inhibition period T3. When the time is shorter than the time (T1 + T3), the energization pulse is turned off during the A / D conversion process, and there is a problem that an accurate A / D conversion value cannot be taken.
[0006]
The present invention has been made in consideration of such circumstances. Therefore, the object of the present invention is to perform A / D conversion in synchronization with the cycle of duty control and to turn off the energization pulse during the A / D conversion process. It is an object of the present invention to provide an energization control device that can prevent this in advance and can always capture an accurate A / D conversion value.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the energization control apparatus according to claim 1 of the present invention activates the A / D conversion means by the A / D activation means after the elapse of a predetermined time from the ON timing of the energization pulse to the load. The D activation means stops activation of the A / D conversion means when the energization pulse width calculated by the duty control means is shorter than the time required for A / D conversion by the A / D conversion means.
[0008]
Conventionally, since the duty control cycle and the A / D conversion execution cycle are not synchronized, when the energization pulse width becomes shorter than T1 + T3 (see FIG. 6), the energization pulse is turned off during the A / D conversion process. However, in the present invention, in order to perform A / D conversion synchronized with the duty control period, the input of the A / D conversion means is performed from the on-timing of the energization pulse. Since the A / D conversion means is activated after a predetermined time until the signal becomes stable, the A / D conversion means can always be activated in the shortest time from the ON timing of the energization pulse. As a result, if the energization pulse width is equal to or greater than T3 (A / D stabilization time + A / D conversion process time), the A / D conversion process can be completed during the ON period of the energization pulse.
[0009]
Further, when the energization pulse width calculated by the duty control means is shorter than the time necessary for performing A / D conversion, it is preferable to stop the A / D conversion means from being activated. In this way, deviation of the duty ratio can be prevented, and the accuracy of duty control can be kept good.
[0010]
In this case, when the start / stop of the A / D conversion means is continued a plurality of times as in claim 2, the energization pulse width is increased to the time required for performing A / D conversion when a predetermined condition is satisfied. You may make it let it. In other words, if the start / stop of the A / D conversion means is continuously generated, new A / D conversion values cannot be taken in, and the control using the A / D conversion values is hindered. Sometimes the energization pulse width is increased to the time required to perform A / D conversion to forcibly perform A / D conversion. Thereby, even when A / D conversion is stopped many times, a new A / D conversion value can be taken in as appropriate. Note that, as the predetermined condition, for example, the number of continuous start / stops of the A / D conversion means, the load control status, the necessity of updating the A / D conversion value, and the like can be considered.
[0011]
Furthermore, when the energization pulse width is increased to the time necessary for A / D conversion as in claim 3, it is preferable to decrease the energization pulse width from the next time onward according to the increase. . In this way, even if the duty ratio shifts in the increasing direction due to the forced A / D conversion, the total energization time can be made constant by the subsequent energization pulse width reduction process. The accuracy is not reduced.
[0013]
The present invention described above can be applied to various energization control devices that perform energization control by duty control. As in claim 5, the elements of the air-fuel ratio sensor installed in the exhaust pipe of the internal combustion engine are heated. You may apply to the energization control of the heater to perform. Thereby, the current and voltage of the heater can be A / D converted with high accuracy, and the power control of the heater and the abnormality diagnosis of the air-fuel ratio sensor can be performed with high accuracy.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment in which the present invention is applied to a heater energization control device for an air-fuel ratio sensor will be described below with reference to FIGS. First, the configuration of the entire system will be described with reference to FIG. An intake pipe 12 of an engine 11 that is an internal combustion engine is provided with a throttle valve (not shown), a fuel injection valve 13 and the like, and an exhaust pipe 14 is provided with a catalyst 15 for purifying exhaust gas. An air-fuel ratio sensor 16 that detects the air-fuel ratio of the exhaust gas is provided on the upstream side. Since the element of the air-fuel ratio sensor 16 has a high activation temperature and a narrow activation temperature range, it is difficult to maintain the activation temperature range only with the heat of the exhaust gas. Therefore, the air-fuel ratio sensor 16 is provided with a heater 17 so that the element temperature of the air-fuel ratio sensor 16 is maintained within the activation temperature range by heating the heater 17.
[0015]
The energization of the air-fuel ratio sensor 16 to the heater 17 is duty-controlled by an electronic control circuit (hereinafter abbreviated as “ECU”) 18. The ECU 18 is mainly composed of a microcomputer 19, and as its peripheral circuits, an A / D conversion circuit 20 (A / D conversion means), a heater drive circuit 21, an input circuit 22, an output circuit 23, and the like are provided. . The input circuit 22 takes in the output voltage (air-fuel ratio detection signal) of the air-fuel ratio sensor 16 and inputs it to the A / D conversion circuit 20. The microcomputer 19 takes in the output voltage of the air-fuel ratio sensor 16 A / D converted by the A / D conversion circuit 20, detects the air-fuel ratio of the exhaust gas, and feedback-controls the air-fuel ratio based on the detected value.
[0016]
The heater drive circuit 21 duty-drives the heater 17 based on the duty signal from the microcomputer 19 to maintain the element temperature of the air-fuel ratio sensor 16 in the active temperature range, and also applies the current and application of the heater 17 (load). The voltage is detected and the detection signal is output to the A / D conversion circuit 20. The microcomputer 19 takes in the current and applied voltage of the heater 17 A / D converted by the A / D conversion circuit 20, and performs abnormality diagnosis of the heater 17 and calculation of the duty ratio of the heater 17 based on the current and applied voltage. Do. Further, the microcomputer 19 calculates the fuel injection amount and the ignition timing, outputs an injection signal from the output circuit 23 to the fuel injection valve 13 to control the injection operation of the fuel injection valve 13, and outputs the ignition signal to the ignition device 24. To control the ignition operation of the spark plug 25.
[0017]
Further, the microcomputer 19 includes an A / D compare register 26 and an energization control compare register 27, and the start timing (hereinafter referred to as “A”) of the A / D conversion circuit 20 using these two compare registers 26 and 27. / D activation timing) and the off timing (falling timing) of the energization pulse of the heater 17 are set.
[0018]
Next, the relationship between the on / off timing of the energization pulse and the A / D conversion processing timing will be described with reference to FIG. An A / D activation timing is set in the A / D compare register 26 every time the energization pulse is turned on in synchronization with the duty control cycle. At this time, the A / D activation timing is determined when the time from when the energization pulse is turned on until the input signal of the A / D conversion circuit 20 is stabilized (A / D stabilization time) has elapsed. Set to start.
[0019]
After the A / D activation timing is set, when the hardware timer value in the microcomputer 19 matches the value of the A / D compare register 26, the A / D conversion circuit 20 is activated by time coincidence interrupt processing. The input signal is A / D converted. Thus, A / D conversion is performed after the A / D stabilization time has elapsed from the ON timing of the energization pulse in synchronization with the duty control cycle.
[0020]
Thereafter, when the A / D conversion is completed, the energization pulse off timing is set in the energization control compare register 27 (see B and C). Thereafter, when the timer value in the microcomputer 19 matches the value in the energization control compare register 27, the energization pulse is turned off by the time coincidence interrupt process. However, when the duty ratio is 100%, the setting of the off timing of the energization pulse is stopped (see A), and the energization pulse is not turned off and is continued to the energization pulse of the next cycle.
[0021]
When the energization pulse width is shorter than the time required for A / D conversion (A / D stabilization time), the A / D start timing is not set in the A / D compare register 26 (see E). , A / D conversion is stopped. In this case, the off timing of the energization pulse is set in the energization control compare register 27 at the on timing of the energization pulse (see D).
[0022]
The processing described above is executed by the microcomputer 19 according to the flowchart of FIG. This program is started in synchronism with a duty control cycle (on timing of energization pulse), and serves as duty control means in the claims. When this program is started, first, in step 101, the energization pulse is turned on at the on timing of the energization pulse, and energization to the heater 17 is started. Thereafter, in step 102, it is determined whether or not the energization pulse width (energization time) is equal to or longer than the time until the input signal of the A / D conversion circuit 20 is stabilized (A / D stabilization time). If A is equal to or longer than the A / D stabilization time, it is determined that A / D conversion is possible, the process proceeds to step 103, the A / D start timing is set in the A / D compare register 26, and the A / D Wait until the start timing comes (step 104).
[0023]
Thereafter, when the A / D activation timing comes, the process proceeds to step 105, where the A / D conversion circuit 20 is activated to A / D convert the input signal. The processing of these steps 104 and 105 serves as A / D starting means in the claims.
[0024]
During the A / D conversion, the process waits until the A / D conversion is completed in step 106. When the A / D conversion is completed, the process proceeds to step 107, and the A / D conversion value is taken into the microcomputer 19. In step 108, the off timing of the energization pulse is set in the energization control compare register 27. The processing in step 108 serves as an off timing setting means in the claims.
[0025]
Thereafter, the process waits until the energization pulse is turned off (step 109). When the off timing is reached, the process proceeds to step 110, where the energization pulse is turned off. The process of step 110 serves as energization pulse-off means in the claims.
[0026]
If it is determined in step 102 that the energization pulse width is shorter than the A / D stabilization time, A / D conversion is impossible, so A / D conversion processing (steps 103 to 107). Without proceeding to step 108, the off timing of the energization pulse is set in the energization control compare register 27 and waits until the energization pulse is turned off (step 109). Proceeding to 110, the energization pulse is turned off.
[0027]
In this embodiment, considering that the A / D conversion processing time is sufficiently shorter than the A / D stabilization time, it is determined in step 102 whether the energization pulse width is equal to or greater than the A / D stabilization time. However, it is determined whether or not the A / D conversion process is possible. However, in consideration of the A / D conversion process time, the energization pulse width is determined by the difference between the A / D stabilization time and the A / D conversion process time. Whether or not A / D conversion processing is possible may be determined based on whether or not the total time is exceeded.
[0028]
The flowchart of FIG. 3 described above schematically describes the flow of the A / D conversion process of the present embodiment. In the system in which the A / D compare register 26 and the energization control compare register 27 are provided in the microcomputer 19 as in the present embodiment, the A / D conversion process is performed as follows according to the program shown in FIGS. To be implemented.
[0029]
The energization start processing program in FIG. 4 is started in synchronization with the duty control cycle (the energization pulse on timing). When this program is started, first, in step 201, the element temperature of the air-fuel ratio sensor 16 is detected or estimated, and the duty ratio (energization pulse width) of the heater 17 is set so that the element temperature becomes the target temperature (activation temperature). Is calculated. In the next step 202, it is determined whether or not the number of A / D conversion cancellations (that is, the number of times that the energization pulse width <A / D stabilization time) continues for a predetermined number of times. Proceed to step 204.
[0030]
If the A / D conversion is stopped more than a predetermined number of times, the process proceeds to step 203 to forcibly take in a new A / D conversion value, and the energization pulse width is subjected to the lower limit guard process with the A / D stabilization time. Then (that is, set the energization pulse width = A / D stabilization time), the process proceeds to step 204. When the energization pulse width is subjected to the lower limit guard processing with the A / D stabilization time, the energization pulse width from the next time is reduced according to the increment of the energization pulse width, and the total energization time is the same as the initial calculation value. It is adjusted to become. This energization pulse width reduction process is performed in step 201 when this program is started next time.
[0031]
In step 204, it is determined whether or not the energization pulse width is 0 (that is, the duty ratio = 0%). When the energization pulse width is 0, that is, when the heater 17 is not energized, the subsequent processing is not performed. Exit the program. On the other hand, if the energization pulse width> 0, the process proceeds to step 205 where the energization pulse is turned on and energization of the heater 17 is started.
[0032]
Thereafter, in step 206, it is determined whether or not the energization pulse width is equal to or greater than the A / D stabilization time. If the energization pulse width is equal to or greater than the A / D stabilization time, it is determined that A / D conversion is possible. In step 207, the A / D activation timing is set in the A / D compare register 26. At this time, the A / D activation timing is set so that the A / D conversion circuit 20 is activated when the A / D stabilization time has elapsed from the ON timing of the energization pulse. After the A / D activation timing is set, when the timer value in the microcomputer 19 coincides with the value of the A / D compare register 26, the A / D conversion circuit 20 is activated by the time coincidence interrupt process and the input signal Is A / D converted.
[0033]
On the other hand, if it is determined in step 206 that the energization pulse width is shorter than the A / D stabilization time, the process proceeds to step 208 and the energization pulse off timing is set in the energization control compare register 27. In this case, the A / D activation timing is not set in the A / D compare register 26, and A / D conversion is not performed.
[0034]
The A / D conversion end processing program in FIG. 5 is started in synchronization with the end of A / D conversion. When this program is started, first, at step 301, it is determined whether or not the duty ratio is less than 100%. If it is less than 100%, the routine proceeds to step 302 and the energization pulse compare timing 27 is turned off. Then, the A / D conversion value is taken into the microcomputer 19 (step 303). Thereafter, when the timer value in the microcomputer 19 matches the value in the energization control compare register 27, the energization pulse is turned off by the time coincidence interrupt process.
[0035]
On the other hand, if it is determined in step 301 above that the duty ratio is 100% (that is, when the heater 17 is energized continuously), the A / The D conversion value is taken into the microcomputer 19 (step 303). When the duty ratio is 100%, the off timing of the energization pulse may be set longer than the actual time corresponding to 100%. In this case, the heater 17 can be energized continuously.
[0036]
According to the present embodiment described above, since the A / D conversion circuit 20 is started when the A / D stabilization time has elapsed from the ON timing of the energization pulse, it is always the shortest time from the ON timing of the energization pulse. Thus, the A / D conversion circuit 20 can be started, and the A / D conversion process can be completed during the ON period of the energization pulse even if the energization pulse width is shorter than the conventional one. In addition, since the off timing of the energization pulse is set at the end of A / D conversion, the energization pulse is not turned off during the A / D conversion process even if the A / D conversion process is delayed due to a processing delay or the like. The problem that the energization pulse is turned off during the A / D conversion process can be solved, and an accurate A / D conversion value can always be captured.
[0037]
In the present embodiment, the A / D conversion is stopped when the energization pulse width is shorter than the A / D stabilization time. However, when the A / D conversion stop continues for a predetermined number of times, the energization pulse Since the lower limit guard processing is performed on the width with the A / D stabilization time, the A / D conversion can be forcibly performed and the A / D conversion value can be updated. In addition, when the energization pulse width is subjected to the lower limit guard process with the A / D stabilization time, the energization pulse width is reduced from the next time according to the increase of the energization pulse width. Even if the duty ratio is shifted in the increasing direction by the implementation, the total energization time can be made constant by subsequent energization pulse width reduction processing, and the accuracy of the duty control does not need to be lowered.
[0038]
Further, conventionally, as shown in FIG. 6, since the duty control cycle is an integer n times the determination cycle T1, there is a drawback that the resolution of the duty control becomes as coarse as 1 / n. , N must be increased to increase the period. On the other hand, in this embodiment, since the off timing of the energization pulse is controlled using the compare coincidence output, the resolution can be increased without increasing the duty control cycle. Therefore, the accuracy of duty control can be improved even if the duty control cycle is made shorter than before.
[0039]
In this embodiment, the microcomputer 19 is provided with two compare registers 26 and 27 for A / D and energization control. However, a single compare register may be used. When using a single compare register, the A / D activation timing may be set in the compare register, and the value of the compare register may be rewritten to the off timing of the energization pulse at the end of A / D conversion.
[0040]
Further, the function of the compare register may be realized by software without using the compare register. Alternatively, as the microcomputer 19, a microcomputer having a port with a time coincidence detection function is used, the port is used as a heater driving port, the off timing of the energization pulse is set in the port compare register, and the timer When the value of the port coincides with the value of the port compare register, the output of the port may be turned off by hardware in the microcomputer.
[0041]
In this embodiment, the A / D activation timing is set after the A / D stabilization time has elapsed from the energization pulse on timing. However, the A / D activation timing is the energization pulse off timing after the A / D stabilization time has elapsed. You may change suitably in the period until. Further, in consideration of the A / D conversion processing time, the A / D activation timing is within a period from (A / D stabilization time + A / D conversion processing time) to (energization pulse width−A / D conversion processing time). May be set as appropriate. In this way, the A / D conversion process can be completed during the ON period of the energization pulse without shifting the OFF timing of the energization pulse.
[0042]
In addition, the application range of the present invention is not limited to the energization control of the heater 17 of the air-fuel ratio sensor 16, but can be implemented by applying the present invention to various energization control devices that perform the energization control by duty control.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an entire system showing an embodiment of the present invention. FIG. 2 is a time chart for explaining the relationship between energized pulse on / off timing and A / D conversion processing timing. FIG. 4 is a flowchart for schematically explaining the flow of the D conversion processing. FIG. 4 is a flowchart for explaining the processing flow of the energization start processing program. FIG. 5 is a flowchart for explaining the processing flow of the A / D conversion end processing program. Time chart for explaining the relationship between the on / off timing of the energized pulse and the A / D conversion processing timing
11 ... Engine (internal combustion engine),
14 ... exhaust pipe,
16: Air-fuel ratio sensor,
17 ... heater (load),
19: Microcomputer (duty control means, A / D starting means, off timing setting means, energization pulse off means),
20 A / D conversion circuit (A / D conversion means),
26: A / D compare register,
27: Compare register for energization control.

Claims (4)

In an energization control device comprising duty control means for duty-controlling energization to a load, and A / D conversion means for A / D converting load current or load voltage during an ON period of the energization pulse to the load,
A / D starting means for starting the A / D conversion means after elapse of a predetermined time from the ON timing of the energization pulse,
When the energization pulse width calculated by the duty control means is shorter than the time required for A / D conversion by the A / D conversion means, the A / D activation means An energization control device characterized by stopping activation. The duty control means performs A / D conversion of the energization pulse width by the A / D conversion means when a predetermined condition is satisfied when the start / stop of the A / D conversion means is continued a plurality of times. The energization control device according to claim 1, wherein the energization control device is increased to a necessary time. When the duty control means increases the energization pulse width to the time necessary for A / D conversion by the A / D conversion means, the duty control means sets the energization pulse width from the next time according to the increase. The energization control device according to claim 2, wherein the energization control device is decreased. The energization control apparatus according to any one of claims 1 to 3, wherein the load is a heater that heats an element of an air-fuel ratio sensor installed in an exhaust pipe of an internal combustion engine .

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