Accelerator opening degree detection apparatus

The accelerator opening degree detection apparatus of the present invention includes: an accelerator pedal position sensor for detecting a position of an accelerator pedal; and a calculating section for calculating an accelerator opening degree based on an output of the accelerator pedal position sensor. The calculating section performs at least the following steps of: obtaining a signal PDLAD by smoothing the output of the accelerator pedal position sensor with a first smoothing coefficient; obtaining a signal PDLSM by smoothing the output of the accelerator pedal position sensor with a second smoothing coefficient which is larger than the first smoothing coefficient; storing a reference value GPDL representing a reference position of the accelerator pedal position sensor; calculating an accelerator opening degree PDLA based on a difference between the signal PDLAD and the reference value GPDL; and updating the reference value GPDL based on the signal PDLSM if the accelerator opening degree PDLA satisfies a predetermined update condition.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to an accelerator opening degree detection 
apparatus for detecting an accelerator opening degree. 
Description of the Related Art 
Japanese Laid-Open Publication No. 61-8433 discloses the techniques of 
providing an accelerator totally closing switch and to determine a 
reference point (i.e., a zero point) of an accelerator pedal position 
sensor based on a signal representing the ON/OFF states of the accelerator 
totally closing switch. 
In accordance with the techniques disclosed in Japanese Laid-Open 
Publication No. 61-8433, an accelerator totally closing switch is required 
to be provided separately from an accelerator pedal position sensor. Thus, 
the technique has a problem in that the costs are adversely increased. In 
addition, if the accelerator totally closing switch is out of order, then 
a problem is caused in that the reference position (zero point) of the 
accelerator pedal position sensor cannot be precisely determined. 
SUMMARY OF THE INVENTION 
The accelerator opening degree detection apparatus of the present invention 
includes: an accelerator pedal position sensor for detecting a position of 
an accelerator pedal; and a calculating section for calculating an 
accelerator opening degree based on an output of the accelerator pedal 
position sensor. The calculating section performs at least the following 
steps of: obtaining a signal PDLAD by smoothing the output of the 
accelerator pedal position sensor with a first smoothing coefficient; 
obtaining a signal PDLSM by smoothing the output of the accelerator pedal 
position sensor with a second smoothing coefficient which is larger than 
the first smoothing coefficient; storing a reference value GPDL 
representing a reference position of the accelerator pedal position 
sensor; calculating an accelerator opening degree PDLA based on a 
difference between the signal PDLAD and the reference value GPDL; and 
updating the reference value GPDL based on the signal PDLSM if the 
accelerator opening degree PDLA satisfies a predetermined update 
condition. 
In one embodiment, the reference value GPDL is updated if the accelerator 
opening degree PDLA continuously satisfies the predetermined update 
condition over a predetermined period of time. 
In another embodiment, the calculation section further performs the step of 
prohibiting an increment of the reference value GPDL from exceeding a 
predetermined upper limit value during a predetermined period of time. 
The accelerator opening degree detection apparatus according to another 
aspect of the present invention includes: an accelerator pedal position 
sensor having a first sensor and a second sensor, each of the first sensor 
and the second sensor detecting a position of an accelerator pedal; and a 
calculating section for calculating an accelerator opening degree based on 
an output of the accelerator pedal position sensor. The calculating 
section performs at least the following steps of: obtaining a signal 
PDLAD1 by smoothing the output of the first sensor with a first smoothing 
coefficient; obtaining a signal PDLSM1 by smoothing the output of the 
first sensor with a second smoothing coefficient which is larger than the 
first smoothing coefficient; storing a first reference value GPDL1 
representing a reference position of the first sensor; calculating a first 
accelerator opening degree PDLA1 based on a difference between the signal 
PDLAD1 and the first reference value GPDL1; obtaining a signal PDLAD2 by 
smoothing the output of the second sensor with a third smoothing 
coefficient; obtaining a signal PDLSM2 by smoothing the output of the 
second sensor with a fourth smoothing coefficient which is larger than the 
third smoothing coefficient; storing a second reference value GPDL2 
representing a reference position of the second sensor; calculating a 
second accelerator opening degree PDLA2 based on a difference between the 
signal PDLAD2 and the second reference value GPDL2; updating the first 
reference value GPDL1 based on the signal PDLSM1 if the first accelerator 
opening degree PDLA1 satisfies a first predetermined update condition or 
if the second accelerator opening degree PDLA2 satisfies a second 
predetermined update condition; and updating the second reference value 
GPDL2 based on the signal PDLSM2 if the second accelerator opening degree 
PDLA2 satisfies the second predetermined update condition. 
Thus, the invention described herein makes possible the advantage of 
providing an accelerator opening degree detection apparatus which can 
precisely determine the reference position of an accelerator pedal 
position sensor without providing an accelerator totally closing switch. 
This and other advantages of the present invention will become apparent to 
those skilled in the art upon reading and understanding the following 
detailed description with reference to the accompanying figures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Hereinafter, the embodiments of the present invention will be described 
with reference to the accompanying drawings. 
Embodiment 1 
FIG. 1 shows a configuration of an accelerator opening degree detection 
apparatus 1 in a first embodiment of the present invention. The 
accelerator opening degree detection apparatus 1 includes an accelerator 
pedal position sensor 10 and an electronic control unit (ECU) 20. 
The accelerator pedal position sensor 10 detects the position of the 
accelerator pedal 6 based on the amount by which the accelerator pedal 6 
has been depressed, thereby outputting a detection signal representing the 
position of the accelerator pedal 6 to the ECU 20. The accelerator pedal 
position sensor 10 may be implemented as a potentiometer, for example. 
The ECU 20 includes: an analog-to-digital (A/D) converter 21; a CPU 22; a 
driver circuit 23; a read-only memory (ROM) 24; a random access memory 
(RAM) 25; and a standby RAM 26. The CPU 22, the ROM 24, the RAM 25 and the 
standby RAM 26 are coupled to each other via a bus 27. 
The A/D converter 21 converts the detection signal, output from the 
accelerator pedal position sensor 10 as an analog value, into a digital 
value. The detection signal converted into the digital value (hereinafter, 
referred to as a signal VPA) is input to the CPU 22. 
In response to the signal VPA, the CPU 22 calculates an accelerator opening 
degree PDLA and then outputs the accelerator opening degree PDLA to the 
driver circuit 23. The accelerator opening degree PDLA is calculated based 
on a reference value GPDL representing the reference position of the 
accelerator pedal position sensor 10. 
The driver circuit 23 drives an actuator 30 based on the accelerator 
opening degree PDLA. The actuator may be a motor for controlling the 
opening degree of a throttle valve, for example. 
FIG. 2 illustrates an accelerator opening degree detection process 
procedure. The accelerator opening degree detection process is stored in 
the form of a program in the ROM 24. The CPU 22 reads out the program for 
the accelerator opening degree detection process and executes the program 
every time a predetermined time has passed. 
Hereinafter, the accelerator opening degree detection process will be 
described step by step with reference to FIG. 2. 
First, in Step S31, the CPU 22 smooths the signal VPA with a first 
smoothing coefficient, thereby obtaining a signal PDLAD. The signal PDLAD 
may be obtained by executing the following recurrence formula (1), for 
example. 
EQU PDLAD.sub.i =PDLAD.sub.i-1 +(VPA-PDLAD.sub.i-1)/2 (1) 
In this case, the CPU 22 stores PDLAD.sub.i which was updated most recently 
as the signal PDLAD in the RAM 25. In the example shown in formula (1), 
the first smoothing coefficient is 2. 
In Step S32, the CPU 22 smooths the signal VPA with a second smoothing 
coefficient larger than the first smoothing coefficient, thereby obtaining 
a signal PDLSM. The signal PDLSM may be obtained by executing the 
following recurrence formula (2), for example. 
EQU PDLSM.sub.i =PDLSM.sub.i-1 +(VPA-PDLSM.sub.i-1)/32 (2) 
In this case, the CPU 22 stores PDLSM.sub.i which was updated most recently 
as the signal PDLSM in the RAM 25. In the example shown in formula (2), 
the second smoothing coefficient is 32. 
In Step S33, the CPU 22 calculates the accelerator opening degree PDLA 
based on a difference between the signal PDLAD and a reference value GPDL 
representing the reference position of the accelerator pedal position 
sensor 10. Before the accelerator opening degree detection process is 
started, the reference value GPDL is set at an initial value. The 
reference value GPDL is stored in the standby RAM 26 such that the 
reference value GPDL is not erased but held therein even after the 
ignition has been turned OFF. The accelerator opening degree PDLA may be 
calculated based on the following equation (3), for example. 
EQU PDLA=PDLAD-GPDL (3) 
In Step S34, the CPU 22 determines whether or not the accelerator opening 
degree PDLA calculated in Step S33 satisfies a predetermined update 
condition. The predetermined update condition may be given by the 
following inequality (4). 
EQU PDLA.ltoreq.PDLA.sub.TH (4) 
where PDLA.sub.TH is a predetermined value indicating that PDLA is in the 
vicinity of the reference position. PDLA.sub.TH is a predetermined value, 
for example, from 1.degree. to 2.degree., both inclusive. 
Alternatively, in Step S34, a predetermined update condition may be a 
condition that the condition given by the inequality (4) is continuously 
satisfied over a predetermined period of time. This is because it takes a 
relatively long time for the value (i.e., the signal PDLSM) which has been 
smoothed with the second smoothing coefficient to catch up with the value 
(i.e., the signal PDLAD) which has been smoothed with the first smoothing 
coefficient. 
If the decision result in Step S34 is "Yes", the process proceeds to Step 
S35. On the other hand, if the decision result in Step S34 is "No", the 
process skips Step S35 and ends. 
In Step S35, the CPU 22 updates the reference value GPDL based on the 
signal PDLSM. The reference value GPDL may be updated based on the 
following recurrence formula (5), for example. 
EQU GPDL.sub.i =GPDL.sub.i-1 +(PDLSM-GPDL.sub.i-1)/32 (5) 
In this case, the CPU 22 stores GPDL.sub.i which was updated most recently 
as the reference value GPDL in the standby RAM 26. 
Alternatively, the reference value GPDL may be updated based on the 
following equation (6). 
EQU GPDL=PDLSM (6) 
In this way, in the accelerator opening degree detection process, the 
reference value GPDL is updated if the accelerator opening degree PDLA 
satisfies a predetermined update condition. Thus, the reference position 
of the accelerator pedal position sensor 10 can be determined without 
providing an accelerator totally closing switch. 
Furthermore, the reference value GPDL is updated based on a value (i.e., 
the signal PDLSM) which has been smoothed by the second smoothing 
coefficient larger than the first smoothing coefficient. This makes it 
possible to prevent the reference position of the accelerator pedal 
position sensor 10 from being erroneously determined owing to the mixture 
of noises and the like. Furthermore, the accelerator opening degree PDLA 
is calculated based on a value (i.e., the signal PDLAD) which has been 
smoothed by the first smoothing coefficient smaller than the second 
smoothing coefficient. This makes it possible to detect a quick operation 
of the accelerator pedal 6. 
FIG. 3 illustrates a modified accelerator opening degree detection process 
procedure. This modified accelerator opening degree detection process 
procedure is provided for preventing the reference position of the 
accelerator pedal position sensor 10 from being erroneously determined in 
the case where the accelerator pedal has been depressed very slowly. 
The accelerator opening degree detection process procedure illustrated in 
FIG. 3 is the same as the accelerator opening degree detection process 
procedure shown in FIG. 2 except that Steps S41 to S44 are additionally 
provided. Thus, the same process steps will be identified by the same 
reference numerals and the description thereof will be omitted herein. 
In Step S41, the CPU 22 determines whether or not the following condition 
expressed by the inequality (7) is satisfied. 
EQU PDLSM.ltoreq.GPDLMN+F (7) 
where GPDLMN represents the minimum value of the reference value GPDL 
during a period T.sub.1. The period T.sub.1 is a period between the 
turn-ON of the ignition and the turn-OFF of the ignition, for example. 
Alternatively, the period T.sub.1 may be a period between the actuation of 
an engine and the stop of the engine. It is noted that the minimum value 
GPDLMN is initialized to be equal to the reference value GPDL at the time 
of the turn ON of the ignition. In addition, F represents a predetermined 
upper limit value. 
If the condition expressed by the inequality (7) is satisfied in Step S41, 
the process proceeds to Step S42 via Step S35. 
In Step S42, the CPU 22 determines whether or not the following condition 
expressed by the inequality (8) is satisfied. 
EQU GPDL&lt;GPDLMN (8) 
where GPDL represents the reference value updated in Step S35. 
If the condition expressed by the inequality (8) is satisfied in Step S42, 
the process proceeds to Step S43. On the other hand, if the condition 
expressed by the inequality (8) is not satisfied in Step S42, the process 
skips Step S43 and ends. 
In Step S43, the CPU 22 updates the minimum value GPDLMN of the reference 
value GPDL during the period T.sub.1 into the reference value GPDL updated 
in Step S35. 
If the condition expressed by the inequality (7) is not satisfied in Step 
S41, the process proceeds to Step S44. 
In Step S44, the CPU 22 updates the reference value GPDL into (GPDLMN+F). 
In this way, the reference value GPDL is controlled such that the increment 
of the updated reference value GPDL does not exceed the predetermined 
value. Thus, even if the accelerator pedal has been depressed very slowly, 
it is possible to prevent the reference position of the accelerator pedal 
position sensor 10 from being erroneously determined. 
FIG. 4A is a timing chart showing a relationship between an actual 
accelerator opening degree and an accelerator opening degree PDLA output 
from the accelerator opening degree detection apparatus 1, while FIG. 4B 
is a timing chart showing a relationship among the signal VPA, the signal 
PDLSM, the signal PDLAD and the reference value GPDL. 
Embodiment 2 
In the second embodiment, a case where the accelerator pedal position 
sensor 10 is a dual sensor will be described. 
FIG. 5 shows a configuration of an accelerator opening degree detection 
apparatus 2 in the second embodiment of the present invention. The 
configuration of the accelerator opening degree detection apparatus 2 
shown in FIG. 5 is the same as that of the accelerator opening degree 
detection apparatus 1 shown in FIG. 1 except that the accelerator pedal 
position sensor 10 includes a main sensor 11 and a sub-sensor 12. Thus the 
same components will be identified by the same reference numerals and the 
description thereof will be omitted herein. 
The main sensor 11 detects the position of the accelerator pedal 6 based on 
the amount by which the accelerator pedal 6 has been depressed, thereby 
outputting a detection signal representing the position of the accelerator 
pedal 6 to the ECU 20. The main sensor 11 may be implemented as a 
potentiometer, for example. 
The sub-sensor 12 also detects the position of the accelerator pedal 6 
based on the amount by which the accelerator pedal 6 has been depressed, 
thereby outputting a detection signal representing the position of the 
accelerator pedal 6 to the ECU 20. The sub-sensor 12 may also be 
implemented as a potentiometer, for example. 
The A/D converter 21 converts the detection signal, output from the main 
sensor 11 as an analog value, into a digital value. The detection signal 
converted into the digital value (hereinafter, referred to as a signal 
V) is input to the CPU 22. 
The A/D converter 21 also converts the detection signal, output from the 
sub-sensor 12 as an analog value, into a digital value. The detection 
signal converted into the digital value (hereinafter, referred to as a 
signal V) is also input to the CPU 22. 
The CPU 22 executes the accelerator opening degree detection process for 
the main sensor 11 and executes the accelerator opening degree detection 
process for the sub-sensor 12. 
The accelerator opening degree detection process for the main sensor 11 is 
the same as the accelerator opening degree detection process shown in FIG. 
2 or 3, except that the signal VPA is replaced with the signal V and 
that Step S34 is replaced with Step S34' to be described below. 
In Step S34', the CPU 22 determines whether or not the accelerator opening 
degree PDLA1 calculated for the main sensor 11 satisfies a first 
predetermined update condition, and also determines whether or not the 
accelerator opening degree PDLA2 calculated for the sub-sensor 12 
satisfies a second predetermined update condition. In this case, the first 
predetermined update condition may be a condition that a state indicating 
that the accelerator opening degree PDLA1 calculated for the main sensor 
11 is in the vicinity of the reference position lasts for a predetermined 
period of time. Similarly, the second predetermined update condition may 
be a condition that a state indicating that the accelerator opening degree 
PDLA2 calculated for the sub-sensor 12 is in the vicinity of the reference 
position lasts for a predetermined period of time. 
If the accelerator opening degree PDLA1 calculated for the main sensor 11 
satisfies the first predetermined update condition, or if the accelerator 
opening degree PDLA2 calculated for the sub-sensor 12 satisfies the second 
predetermined update condition, the CPU 22 updates the reference value 
GPDL1 representing the reference position of the main sensor 11 in Step 
S35. 
The accelerator opening degree detection process for the sub-sensor 12 is 
the same as the accelerator opening degree detection process shown in FIG. 
2 or 3, except that the signal VPA is replaced with the signal V. The 
CPU 22 updates the reference value GPDL2 representing the reference 
position of the sub-sensor 12 in Step S35 if the accelerator opening 
degree PDLA2 calculated for the sub-sensor 12 satisfies the second 
predetermined update condition. 
In this way, the reference value GPDL1 representing the reference position 
of the main sensor 11 is updated if at least one of the update condition 
for the main sensor 11 and the update condition for the sub-sensor 12 has 
been satisfied. Thus, it is possible to reduce the possibility of 
erroneously determining the reference position of the main sensor 11. 
According to the accelerator opening degree detection apparatus of the 
present invention, the reference value GPDL is updated if the accelerator 
opening degree PDLA satisfies a predetermined update condition. Thus, the 
reference position of the accelerator pedal position sensor can be 
determined without providing an accelerator totally closing switch. In 
addition, the reference value GPDL is updated based on the signal PDLSM 
which has been smoothed with a second smoothing coefficient larger than a 
first smoothing coefficient. Consequently, it is possible to prevent the 
reference position of the accelerator pedal position sensor from being 
erroneously determined owing to the mixture of noises and the like. 
Furthermore, the accelerator opening degree PDLA is calculated based on 
the signal PDLAD which has been smoothed with the first smoothing 
coefficient smaller than the second smoothing coefficient. Consequently, 
it is possible to detect a quick operation of the accelerator pedal. 
Moreover, the reference value GPDL may be updated if the accelerator 
opening degree PDLA continuously satisfies the predetermined update 
condition over a predetermined period of time. This makes it possible to 
improve the precision of the reference value GPDL. This is because it 
takes a relatively long time for the signal PDLSM which has been smoothed 
with the second smoothing coefficient to catch up with the signal PDLAD 
which has been smoothed with the first smoothing coefficient. 
Furthermore, the increment of the reference value GPDL may be prohibited 
from exceeding a predetermined upper limit value during a predetermined 
period. Thus, even if the accelerator pedal has been depressed very 
slowly, it is possible to prevent the reference position of the 
accelerator pedal position sensor from being erroneously determined. 
According to another aspect of the accelerator opening degree detection 
apparatus of the present invention, the reference value GPDL1 representing 
the reference position of the first sensor is updated if the first 
accelerator opening degree PDLA1 of the first sensor satisfies the first 
predetermined update condition or if the second accelerator opening degree 
PDLA2 of the second sensor satisfies the second predetermined update 
condition. This makes it possible to reduce the possibility of erroneously 
determining the reference position of the first sensor. 
Various other modifications will be apparent to and can be readily made by 
those skilled in the art without departing from the scope and spirit of 
this invention. Accordingly, it is not intended that the scope of the 
claims appended hereto be limited to the description as set forth herein, 
but rather that the claims be broadly construed.