Method and apparatus for controlling throttle valve

An apparatus for controlling an opening of a throttle valve to adjust an amount of air flow led into an internal combustion engine mounted on a vehicle. A depression sensor detects the degree of depression of an accelerator pedal. An electric component is provided for electrically adjusting the opening of the throttle valve based on the depression of the gas pedal. A mechanical component is provided for adjusting the opening of the throttle valve in response to the depression of the accelerator pedal. The mechanical component is rendered operable when the electric component fails to control the opening of the throttle valve. An electric control unit (ECU) prohibits the electric component from resuming control of the throttle valve until a certain condition is met, such as stoppage of the engine or the entire vehicle, even if the electric component is capable of controlling the throttle valve. In another embodiment, the ECU prohibits the electric component from resuming control of the throttle valve until a transmission shift position of neutral or park is detected.

BACKGROUND OF THE INVENTION 
The present invention generally relates to an apparatus for controlling a 
throttle valve in vehicles. More particularly, the present invention 
pertains to a throttle valve controlling apparatus that includes a 
component for electrically controlling the opening of a throttle valve and 
a component for mechanically controlling the throttle valve when the 
electric component fails to control the throttle valve. 
A typical engine has throttle valve provided in its intake air pipe to 
control the amount of air drawn into the engine. In one system for 
controlling the throttle valve opening TA, the throttle valve is coupled 
to a gas pedal by a wire. The throttle opening TA is mechanically 
controlled in accordance with the degree of gas pedal depression PA. 
Therefore, there is a one-to-one relationship between the throttle opening 
TA and the gas pedal depression amount PA at any given running state of 
the engine. 
Recently, apparatuses for electrically controlling the throttle opening TA 
have been proposed. This type of apparatus includes a computer for 
computing a target throttle opening based on the degree of gas pedal 
depression PA and several parameters indicating the running state of the 
engine. The computer controls an actuator (for example, an electric motor) 
of the throttle valve such that the throttle opening TA matches a target 
throttle opening. 
In this type of throttle apparatus, the relationship between the throttle 
opening TA and the gas pedal depression amount PA is arbitrarily 
determined. In other words, the throttle opening TA can be altered such 
that the opening TA is suitable for the running state of the engine, and 
is not necessarily directly proportional to the degree of pedal 
depression. 
However, when a malfunction occurs in the throttle valve, for example, if 
the throttle valve sticks to the wall of the intake pipe due to deposits 
formed in the pipe, the actuator may fail to properly control the throttle 
opening TA. 
Japanese Examined Patent Publication No. 8-23312 discloses an apparatus for 
dealing with this problem. This apparatus has a mechanical component that 
couples a gas pedal with to the throttle valve with a wire. When the 
actuator fails to control the throttle opening TA, the mechanical 
component takes over the control of the throttle opening TA. FIG. 9 
illustrates a throttle valve controlling apparatus that includes such a 
mechanical component. 
This apparatus includes a shaft 81 rotatably supported in an intake air 
pipe 80, a throttle valve 82 secured to the shaft 81, a motor 83 for 
controlling the opening of the valve 82, a controller 84, a sensor 85 for 
detecting the degree of depression of the gas pedal, and a sensor 86 for 
detecting opening or the throttle valve 82. The controller 84 computes a 
target throttle opening based on a signal from the gas pedal sensor 85 and 
actuates the motor 83 such that the throttle opening TA detected by the 
sensor 86 matches the target opening. 
The shaft 81 is secured to a first lever 87, which is urged by a spring 88 
in a direction closing the throttle valve 82. A second lever 89, which is 
rotatably supported on the shaft 81, is coupled to a third lever 91 by a 
wire 90. Pressing the gas pedal 92 over a predetermined amount causes the 
pedal 92 to contact the third lever 91 thereby drawing the wire 90. This 
causes the second lever 89 to contact the first lever 87 and rotates the 
first lever 87 integrally with the second lever 89 against the force of 
the spring 88. In this manner, the throttle valve 82 is opened by 
manipulation of the gas pedal 92. 
If the throttle valve 82 sticks to the inner wall of the intake air pipe 
80, it is assumed that, even if actuated by the controller 84, the motor 
83 will fail to change the throttle opening TA. The controller 84 then 
judges that the valve 82 is stuck on the inner wall of the pipe 80 and 
controls the motor 83 to generate the maximum torque. The force of the 
maximum torque of the motor 83 alone or the combined force of the maximum 
torque and rotational force applied on the shaft 81 by cooperation of the 
levers 87, 89 and 91 increases the throttle opening TA. When the increase 
in the throttle opening TA is detected by the throttle opening sensor 86, 
the controller 84 judges that the valve 82 is free from the inner wall of 
the pipe 80. From the time of this judgment, the controller 84 temporarily 
stops controlling the valve 82 with the motor 83 until the gas pedal 92 is 
separated from the third lever 91 by the driver's manipulation of the 
pedal 92. 
In this manner, the apparatus frees the throttle valve 82 from the wall of 
the pipe 80. At this time, the controller 84 stops controlling the 
throttle valve 82 with the motor 83. Therefore, even if the driver 
significantly increases the pedal depression PA, the opening TA of the 
valve 82 is not increased accordingly. This keeps the engine speed lower 
than the speed that corresponds to the increased amount of pedal 
depression PA when the valve 82 is actuated by the motor 83. 
However, this apparatus has the following drawbacks. 
The throttle opening TA is increased for freeing the valve 82 from the wall 
of the pipe 80. Therefore, when the motor 83 resumes controlling the 
throttle valve 82 after the valve 82 is controlled by the levers 87, 89 
and 91, the vehicle is likely to be moving. This may result in an 
unpredictable running state of the vehicle. 
That is, the same amount of depression of the gas pedal 92 results in 
different openings of the throttle valve 82 at a time immediately before 
the motor 83 resumes controlling the valve 82 and at a time immediately 
after the motor 83 resumes controlling the valve 82. Therefore, if the 
valve 82 sticks to the pipe 80 and is thereafter freed, the driver may be 
disturbed due to the unexpected change in the relationship between the 
degree of depression of the gas pedal 92 and the engine speed. 
SUMMARY OF THE INVENTION 
Accordingly, it is an objective of the present invention to prevent a 
driver from experiencing uncomfortable and unpredictable relationship 
between depression amount of a gas pedal and the engine speed when an 
electric component resumes controlling the throttle valve after a 
mechanical component controls the opening of the throttle valve. 
To achieve above objective, the present invention provides an apparatus for 
controlling the opening of a throttle valve to adjust the amount of air 
flow to an internal combustion engine mounted on a vehicle. An 
acceleration pedal is arranged to be depressed by a driver. A depression 
sensor is provided for detecting the degree of depression of the 
acceleration pedal. An electric component is provided for adjusting the 
opening of the throttle valve with an electric power source based on the 
detected degree of depression of the acceleration pedal. A mechanical 
component is provided for adjusting the opening of the throttle valve in 
response to the degree of depression of the acceleration pedal. The 
mechanical component is rendered operable when the electric component 
fails to control the opening of the throttle valve. A first sensor is 
provided for detecting a predetermined condition of the vehicle. A 
controller device is provided for returning control of the throttle valve 
to the electric component, after a period of control of the throttle valve 
by the mechanical component, only when the predetermined condition is 
detected by the first sensor. 
Other aspects and advantages of the invention will become apparent from the 
following description, taken in conjunction with the accompanying 
drawings, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention will now be described with 
reference to FIGS. 1 to 4. 
As shown in FIG. 1 a multi-cylinder gasoline engine 12 mounted on a vehicle 
11 includes a cylinder block 13 and a cylinder head 14. A plurality of 
cylinder bores 15 (only one is shown) are defined in the cylinder block 
13. A piston 16 is located in each cylinder bore 15. A connecting rod 17 
couples each piston 16 to a crankshaft (not shown). Reciprocation of the 
pistons 16 is converted into rotation of a crankshaft by the rod 17. 
Each cylinder bore 15, cylinder head 14 and each piston 16 define a 
combustion chamber 18. A plurality of intake ports 19 (only one is shown) 
and a plurality of exhaust port 20 (only one is shown) are defined in the 
cylinder head 14. Each suction port 19 and each exhaust port 20 are 
communicated with one of the combustion chambers 18. A suction valve 21 
selectively opens and closes each intake port 19. Likewise, an exhaust 
valve 22 selectively opens and closes each exhaust port 20. 
The intake ports 19 are connected to an intake passage 26 by an intake 
manifold 25. A throttle valve 23 and a surge tank 24 are provided in the 
intake passage 26. The intake passage 26 leads the outside air into each 
combustion chamber 18. The upstream side of the valve 23 is connected to 
the downstream side by a bypass passage (not shown). An idle speed control 
valve (next shown) is provided in the bypass passage. When the throttle 
valve 23 is fully closed, the idle speed control valve maintains a certain 
flow of intake air to the engine 12 and thus stabilizes the idling of the 
engine 12. 
The throttle valve 23 is rotatably supported in the intake passage 26 by an 
axle 27. A system for operating the throttle valve 23 includes an electric 
component E and a mechanical component M. The amount of airflow in the 
intake passage 26 (intake amount) is controlled by the inclination of the 
throttle valve 23, or the throttle opening TA. 
The components E and M for actuating the throttle valve 23 will now be 
described with reference to FIG. 2. An electromagnetic clutch 28 is fixed 
to an end (left end as viewed in FIG. 2) of the axle 27. The electric 
motor 29 is operably coupled to the clutch 28 and a throttle valve opening 
sensor 44 is located on the axle 27 between the valve 23 and the clutch 
28. An interlocking lever 30, an intermediate lever 31 and a throttle 
lever 32 are provided on the other side of the axle 27. 
The interlocking lever 30 is fixed to the axle 27 and is urged by a spring 
33 in a direction to open the throttle valve 23. The intermediate lever 31 
rotates relative to the axle 27 and is urged by a spring 34 in a direction 
to close the valve 23. Specifically, the levers 30 and 31 have projections 
30a and 31a, respectively. Rotation of the lever 31 in the direction to 
close the valve 23 is transmitted to the lever 30, which is fixed to the 
axle 27, by contact between the projections 30a and 31a. The moment of the 
lever 31 is greater than the opposite moment of the lever 30. This is 
accomplished by making the spring force of the spring 34 greater than that 
of the spring 33 Therefore, when the clutch 28 is de-activated and 
disconnects the motor 29 from the axle 27, the throttle valve 23 is closed 
by the force of the spring 34. The clutch 28, the motor 29, the 
interlocking lever 30, the intermediate lever 31 and the springs 33, 34 
are included in the electric component E. 
A gas pedal 35 is provided in the passenger compartment of the vehicle 11. 
The pedal 35 pivots about an axis 35a. The throttle lever 32 is rotatably 
supported on the axle 27 and is operably coupled to the gas pedal 35 with 
a wire 36. The throttle lever 32 is urged by a spring 37 in a direction 
closing the throttle valve 23. A projection 32a is formed on the throttle 
lever 32. The projection 32a is normally separated from the intermediate 
lever 31. The throttle lever 32 contacts the intermediate lever 31 only 
when the clutch 28 is de-activated to disconnect the axle 27 from the 
motor 29 and the gas pedal 35 is pressed against the force of the spring 
37 over a predetermined amount (i.e., when the gas pedal depression amount 
PA is equal to or greater than a predetermined value). The throttle lever 
32, the wire 36 and the spring 37 are included in the mechanical component 
M. 
Referring to FIG. 3, the relationship between the gas pedal depression 
amount PA and the throttle opening TA will now be described. The 
continuous diagonal line in FIG. 3 represents the relationship between TA 
and PA when there is no malfunction in the electric component E. 
"Malfunction in the electric component E" in this specification refers to 
a state in which the electric component E is unable to control the 
throttle valve 23 properly. Such a malfunction includes a breakdown of 
throttle sensor 44, the gas pedal sensor 45 or the motor 29. Another cause 
of a malfunction includes sticking of the periphery of the throttle valve 
23 to the inner wall of the intake passage 26 whereby the motor 29 is 
unable to properly rotate the valve 23. As shown in FIG. 3, the throttle 
opening TA is linearly increased in accordance with the increase in the 
gas pedal depression amount PA. 
As illustrated in FIG. 3, the throttle opening TA that corresponds to a 
given gas pedal depression amount PA varies in a range between the broken 
lines in accordance with the running state of the engine 12. For example, 
if the gas pedal depression amount PA is in FIG. 3, the throttle 
opening TA corresponding to the value varies from the minimum value 
TA1min to the maximum value TA1max. 
On the other hand, the alternate long and short dash line in FIG. 3 shown 
the relationship between the throttle opening TA and the gas pedal 
depression amount PA when the throttle valve 23 is actuated by the 
mechanical component M. When the pedal depression amount PA is equal to or 
smaller than a predetermined value , the throttle opening is zero (For 
visibility, the dashed line is a slightly offset from the PA axis). When 
the pedal depression amount PA exceeds the value , the projection 32a 
of the throttle lever 32 contacts the intermediate lever 31 and the 
throttle opening TA is gradually increased. 
As shown in FIG. 3, if the electric component E takes over control of the 
throttle valve 23 from the mechanical component M, the throttle opening TA 
is significantly increased. 
As illustrated in FIG. 1, the intake manifold 25 has a plurality of 
injectors 38 (only one is shown), each of which corresponds to one of the 
combustion chambers 18. Each injector 38 injects fuel toward the 
corresponding intake port 19. The fuel injected by the injectors 38 and 
the airflow form an air-fuel mixture. The mixture is drawn into each 
combustion chambers 18. The cylinder head 14 has a plurality of spark 
plugs 39, each of which corresponds to one of the combustion chambers 18. 
Each spark plug 39 is activated by spark signals distributed by a 
distributor 40. The distributor 40 distributes high voltage from an 
igniter 41 to the spark plugs 39 in synchronization with an angle of the 
crankshaft's rotation. Activating the spark plug 39 burns the air-fuel 
mixture in the combustion chambers 18. The high pressure high temperature 
gas in each chamber 18 causes the piston 16 to reciprocate. The 
reciprocation of the pistons 16 rotates the crankshaft thereby generating 
the power of the engine 12. 
An exhaust passage 43, which includes an exhaust manifold 42 and a 
catalytic converter (not shown), is connected to each exhaust port 20. The 
burned gas in each combustion chamber 18 is discharged from the engine 12 
via the exhaust passages 43. 
The engine 12 is provided with various kinds of sensors that detect the 
running state of the engine 12. The sensors include a throttle valve 
opening sensor 44, a gas pedal sensor 45, an intake pressure sensor 46, a 
rotational speed sensor 47 and a vehicle speed sensor 48. 
The throttle sensor 44 includes a pair of detectors (not shown). Each 
detector detects the throttle opening TA, which is a rotation angle of the 
axle 27 of the valve 23. The gas pedal sensor 45 also includes a pair of 
detectors (not shown). Each detector detects the gas pedal depression 
amount PA. Each pair of the detectors function to detect a malfunction of 
the sensors 44, 45. If the detectors of the throttle sensor 44 issue 
different values of throttle the opening TA, a malfunction of the sensor 
44 is detected. In the same manner, if the detectors of the gas pedal 
sensor 45 issue different values of the gas pedal depression amount PA, a 
malfunction of the sensor 45 is detected. 
The intake pressure sensor 46 detects the intake pressure PM in the intake 
passage 26. The rotational speed sensor 47 detects the crankshaft's 
rotational speed, or the engine speed NE, by referring to the rotation of 
a rotor incorporated in the distributor 40. 
The vehicle 11 also includes an automatic transmission 49 that is operably 
coupled to the engine 12. The selector lever of the transmission 49 is 
selectively switched among a parking position, a reverse position, a drive 
position and a neutral position by the driver. A vehicle speed sensor 48 
is located in the transmission 49 for detecting the speed of the vehicle 
11, that is, the vehicle speed SPD. 
The engine 12 includes a starter (not shown). The starter gives rotational 
force to the engine 12 by cranking and has a starter switch 51 that 
detects ON/OFF state of the starter. As known in the art, the starter is 
turned on or off by manipulation of an ignition switch 52 located in the 
passenger compartment. When the driver manipulates the ignition switch 52, 
the starter is actuated and the starter switch 51 outputs a starter signal 
STA to an electronic control unit 50, which will be described later. When 
the ignition switch 52 is turned off, the engine 12 stops running. Also, a 
warning lamp 53 is provided on the instrument panel for notifying the 
driver of a malfunction of the control of the throttle opening TA. 
The electronic control unit (ECU) 50 controls the actuators, such as the 
electromagnetic clutch 28, the electric motor 28, the injectors 38 and the 
igniters 41. The ECU 50 has a memory 50a, a central processing unit (CPU) 
and I/O ports. The memory 50a stores predetermined control programs and 
data, based on which the CPU 50 performs various computations. The I/O 
ports allow the ECU 50 to transmit data to and receive data from the 
sensors and the actuators. The ECU 50 activates the warning lamp 53 
through the I/O ports. The ECU 50 inputs detected signals from the sensors 
44 to 48 and controls the actuators based on the inputted signals thereby 
controlling the throttle opening TA. 
For example, the ECU 50 computes an optimal throttle opening (a target 
opening TTAH) based on a gas pedal depression amount TA detected by the 
gas pedal sensor 45. The ECU 50 then Actuates the motor 29 such that the 
actual throttle opening TA detected by the throttle valve opening sensor 
44 matches the target opening TTAH. 
Referring to the flowchart of FIG. 4, a throttle opening control routine 
executed by the ECU 50 will be described. The ECU 50 executes this routine 
at predetermined intervals after the engine 12 is started. 
At step 110, the ECU 50 inputs the throttle opening TA, the gas pedal 
depression amount PA, the intake pressure PM, the engine speed NE and 
vehicle speed SPD from the sensors 44 to 48. 
At step 120, the ECU 50 computes a target opening TTAH based on the pedal 
depression amount PA, the intake pressure PM and the engine speed NE. For 
computing TTAH, the ECU 50 refers to function data stored in the memory 
50a. The function data reflects an optimal relationship between the 
parameters PA, PM, NE and the target opening TTAH. 
At step 130, the ECU 50 judges whether an abnormality flag XFAIL has a 
value of one. The abnormality flag XFAIL indicates whether there is a 
malfunction in the electric component E. 
If the flag XFAIL does not have the value of one, that is, if there is no 
malfunction in the electric component E, the ECU 50 moves to step 160. At 
step 160, the ECU 50 executes a normal state control of the throttle valve 
23. That is, the ECU 50 controls the motor 29 with a current value that 
corresponds to the difference between the actual throttle opening TA and 
the target opening TTAH such that the actual throttle opening TA matches 
the target opening TTAH. The throttle valve 23 is thus rotated to decrease 
the difference between the actual throttle opening TA and the target 
opening TTAH. 
At step 170, the ECU 50 judges whether there is a malfunction in the 
electric component E. That is, the ECU 50 judges whether the following 
conditions (1-a) to (1-g) are satisfied. 
Condition (1-a): signals from the pair of detectors in the throttle valve 
opening sensor 44 match each other. If they do not match, one of the 
detectors is judged to be out of order. 
Condition (1-b): signals outputted from the detectors in the throttle valve 
opening sensor 44 are in a predetermined range. If the value of the 
signals is out of the range, within which the value may vary when there is 
no malfunction, it is judged that there is a break in wires that connect 
the detectors of the sensor 44 with the ECU 50. 
Condition (1-c): signals from the pair of detectors in the gas pedal sensor 
45 match each other. If they do not match, one of the detectors is judged 
to be out of order as in the condition (1-a). 
Condition (1-d): signals outputted from the detectors in the gas pedal 
sensor 45 are in a predetermined range. If the condition (1-d): is not 
satisfied, it is judged that there is a break in wires that connect the 
detectors of the sensor 45 with the ECU 50, as in the condition (1-b). 
Condition (1-e): the difference between the throttle opening TA and the 
target opening TTHA is in a predetermined range. If the difference between 
TA and TTHA is not in the predetermined range, the motor 29 is judged not 
to be controlling the throttle opening TA properly. The motor 29 is thus 
judged to be out of order. 
Condition (1-f): the gas pedal depression amount PA and the throttle 
opening TA satisfy a predetermined relationship. If the condition (1-f) is 
not satisfied, the throttle opening TA that corresponds to a given gas 
pedal depression amount PA is out of the range between the broken lines in 
FIG. 3. 
Condition (1-g): the current value through the electric motor 29 is in a 
predetermined rang, if the current value is not in the range, it is judged 
that the throttle valve 23 is stuck on the wall of the intake passage 26 
and an excessive torque is acting on the motor 29. 
If at least one of the conditions (1-a) to (1-g) is not satisfied at step 
170, the ECU 50 judges that there is a malfunction in the electric 
component E. 
If the ECU 50 judges that there is a malfunction in the electric component 
E (if the determination of step 170 is positive), the ECU 50 moves to step 
190. At step 190, the ECU 50 sets the abnormality flag XFAIL to one. 
If the ECU 50 judged that there is no malfunction in the electric component 
E (if the determination of stop 170 is negative), the ECU 50 moves to step 
180. At step 180, the ECU 50 sets the abnormality flag XFAIL to zero. 
If the abnormality flag XFAIL has a value of one at step 130, that is, if 
the electric component E has been judged to have a malfunction in the 
previous routine or earlier, the ECU 50 moves to step 140. 
At step 140, the ECU 50 judges whether a return condition, which will be 
described later, is satisfied. If the return condition is not satisfied, 
the ECU 50 moves to step 150 and executes control steps for a 
malfunctioning state. 
At step 150, the ECU 50 de-activates the electromagnetic clutch 28 and 
stops feeding current to the motor 29. This disconnects axle 27 from the 
drive force of the motor 29. The force of the spring 34 thus directly acts 
on the throttle valve 23. The ECU 50 also lights the warning lamp 53 
thereby notifying the driver of the malfunction in the control of the 
throttle opening TA. 
Satisfaction of the return condition at step 140 refers to the satisfaction 
of the following condition (2-a). 
Condition (2-a): the selector lever of the automatic transmission 49 is in 
the neutral position or in the parking position. 
If the return condition is satisfied at step 140, the ECU 50 moves to step 
160. That is, the ECU 50 does not execute the malfunctioning state control 
of step 150 even if there is a malfunction in the electric component E. 
Instead, the ECU 50 temporarily executes the normal state control at step 
160. Thereafter, the ECU 50 determines whether there is a malfunction in 
the electric component E at step 170 and, based on the determination at 
step 170, sets the value of the abnormality flag XFAIL at step 180 or step 
190. 
After executing the processes of steps 150, 180 or 190, the ECU 50 
temporarily terminates the routine. 
The operation and advantages of the first embodiment will now be described. 
The following example pertains to a case where the throttle valve 23 is 
stuck on the wall of the intake passage 26 and is then freed therefrom. 
That is, the example pertains to a restoration of the normal control 
state. 
Suppose the throttle valve 23 is controlled based on the difference between 
the current throttle opening TA and a target opening TTAH. If the valve 23 
is stuck to the inner wall of the intake passage 26, the conditions (1-e), 
(1-f) and (1-g) are not satisfied. Accordingly, the ECU 50 sets the 
abnormality flag XFAIL to one. As a result, the ECU 50 executes the 
malfunctioning state control of the throttle valve 23. 
During the malfunctioning state control of the valve 23, pressing the gas 
pedal 35 for a predetermined amount or more causes the projection 32a of 
the throttle lever 32 to contact the intermediate lever 31 thereby 
operably coupling the pedal 35 with the valve 23. Accordingly, the 
intermediate lever 31 is rotated by the throttle lever 32 by an amount 
corresponding to the depression amount PA of the gas pedal 35. The 
rotation of the intermediate lever 31 causes the interlocking lever 30 and 
the throttle valve 23 to be rotated by the force of the spring 33 in a 
direction opening the valve 23. 
If the rotational torque of the spring 33 acting on the throttle valve 23 
is great enough to rotate the valve 23 that is stuck on the inner wall of 
the passage 26, the valve 23 is freed from the inner wall. 
In this embodiment, even if the throttle valve 23 is freed from the inner 
wall of the passage 26, the electric component E does not start 
controlling the valve 23 before the return condition is satisfied. That 
is, even if the valve 23 becomes rotatable, the abnormality flag XFAIL is 
still one. Therefore, the ECU 50 continues to execute the malfunctioning 
state control until the return condition (2-a) of step 140 is satisfied. 
When the return condition (2-a) is satisfied, the ECU 50 starts the normal 
state control of the throttle valve 23. Thereafter, the ECU 50 judges 
whether there is a malfunction in the electric component E. In this 
example, the throttle valve 23 is already freed from the inner wall and 
the conditions (1-a) to (1-g) are satisfied. The ECU 50 therefore sets the 
abnormality flag XFAIL to zero. The ECU 50 then resumes the normal state 
control of the throttle valve 23. 
The above example shows a case where the throttle valve 23 is stuck on the 
inner wall of the intake passage 26. Similarly, when any of the motor 29, 
the throttle valve opening sensor 44 or the gas pedal sensor 45 is 
temporarily out of order and thereafter starts functioning again, the 
normal state control of the throttle valve 23 is not executed until the 
return condition is satisfied. If the malfunction in the electric 
component E has already been solved when the return condition is 
satisfied, the normal state control of the throttle valve 23 is executed. 
If the malfunction has not been solved, the malfunctioning state control 
of the valve 23 is continued. 
In the above example, when the throttle valve 23 is freed from the inner 
wall, the gas pedal 35 is pressed by a certain amount and the valve 23 is 
kept open. The vehicle 11 is therefore likely to be moving. If the 
electric component E resumes controlling the opening of the valve 23 in 
this state, the driver may be disturbed by the unexpected change in the 
relationship between the depression amount of the gas pedal 35 and the 
engine speed. In other words, when the electric component E resumes 
controlling the valve 23, the throttle opening TA corresponding to the 
current depression amount PA of the gas pedal 35 is increased (from a 
point on the dashed line to a point between the broken lines in the graph 
of FIG. 3). If the vehicle is moving at this time, the increase in the 
throttle opening TA abruptly increases the engine speed NE thereby 
undesirably accelerating the speed of the vehicle. 
However, according to this embodiment, if the return condition (2-a) is 
satisfied, that is, when the selector lever of the automatic transmission 
49 is in the neutral position or in the parking position, the normal state 
control of the throttle valve 23 is resumed. Thus, even if the engine 
speed NE is unintentionally increased, the increase of the engine speed NE 
does not affect the running condition of the vehicle. This is because the 
power of the engine 12 is not transmitted to the drive system of the 
vehicle 11 when the selector lever of the transmission 49 is either in the 
neutral position or in the parking position. 
As a results the first embodiment positively prevents the driver from 
feeling uncomfortable about the control of the gas pedal 35 when the 
control of the electric component E is resumed while the vehicle is 
running. 
Further, in the first embodiment, the warning lamp 53 is lit when there is 
a malfunction in the electric component E for notifying the driver of the 
malfunction. Thus, the driver can quickly deal with the malfunction. 
A second embodiment of the present invention will now be described. 
To avoid a redundant description, like or same reference numerals are given 
to those components that are the same as the corresponding components of 
the first embodiment. 
The second embodiment is different from the first embodiment in the return 
condition at step 140 of the throttle opening control routine. In the 
first embodiment, the return condition is that the selector lever of the 
automatic transmission 49 is either in the neutral position or in the 
parking position. The return condition of the second embodiment is the 
following condition (2-b). 
Condition (2-b): the gas pedal 35 is not pressed at all (the gas pedal 
depression amount PA is zero) and the vehicle speed SPD is zero. 
If condition (2-b) is satisfied, the ECU 50 allows the electric component E 
to resume the control of the throttle valve 23. Therefore, even if a 
malfunction in the electric component E is solved, the electric component 
E does not resume the control of the throttle valve 23 until the vehicle 
11 is stopped. As a result, the controllability of the gas pedal 35 does 
not change while the vehicle 11 is moving. This embodiment thus positively 
prevents the driver from feeling uncomfortable about the control of the 
gas pedal 35. 
In addition, the electric component E takes over the control of the 
throttle valve 23 when the gas pedal 35 is not pressed. Therefore, the 
throttle valve 23 is fully closed before and after the taking over of 
control. That is, the throttle opening TA does not change at all before 
and after the taking over of control. In this manner, the second 
embodiment prevents the speed of the vehicle from being undesirably 
accelerated by an increase in the throttle opening TA when the electric 
component E resumes the control of the throttle valve 23. 
A third embodiment of the present invention will now be described with 
reference to FIG. 5. 
To avoid a redundant description, like or the same reference numerals are 
given to those components that are like or the same as the corresponding 
components of the first embodiment. 
FIG. 5 is a flowchart showing a throttle opening control routine according 
to the third embodiment. In step having the same numerals as those in FIG. 
4, the ECU 50 performs the same processes as in the first embodiment. The 
ECU 50 executes the routine at predetermined intervals from when the 
engine 12 is started until a predetermined time period has elapsed after 
the engine 12 is stopped. 
At step 111, the ECU 50 inputs the throttle opening TA, the gas pedal 
depression amount PA, the intake pressure PM, the engine speed NE and 
vehicle speed SPD from the sensors 44 to 48. The ECU 50 also inputs the 
starter signal STA from the starter switch 51. If the ECU 50 judges that 
the abnormality flag XFAIL is one at step 130, the ECU 50 moves to the 
step 135. 
At step 135, the ECU 50 judges whether the starter signal STA is ON and an 
engine stop determination flag XOFF has a value of one. The engine stop 
determination flag XOFF indicates whether the engine 12 has been stopped 
after a malfunction occurs in the electric component E. If the conditions 
of step 135 are not satisfied, the ECU 50 moves to step 140. 
At step 140, the ECU 50 judges whether the following return condition (2-c) 
is satisfied. 
Condition (2-c): the ignition switch 52 is at the OFF position. If the 
return condition (2-c) is satisfied (if the determination of step 140 is 
positive), the ECU 50 judges that the engine 12 has been stopped after a 
malfunction occurred in the electric component E and moves to step 145. At 
step 145, the ECU 50 sets the engine stop determination flag XOFF to one. 
If the condition of step 140 is not satisfied, or after executing the 
process of step 145, the ECU 50 moves to step 150 and executes the 
malfunctioning state control of the throttle valve 23. 
If the conditions of step 135 are satisfied, on the other hand, the ECU 50 
moves to step 155. At step 155, the ECU 50 sets the engine stop 
determination flag XOFF to zero. At step 160, the ECU 50 judges that the 
engine 12 is re-started after the occurrence of a malfunction in the 
electric component E and thus temporarily executes the normal state 
control of the throttle valve 23. The ECU 50 judges whether there is a 
malfunction in the electric component E in step 170. At steps 180 or 190, 
the ECU 50 sets the abnormality flag XFAIL to one or zero in accordance 
with the determination result at step 170. 
As described above, even if a malfunction is solved during the 
malfunctioning state control of the throttle valve 23, the normal state 
control of the valve 23 is not resumed until the engine 12 is stopped and 
restarted. Since the vehicle is not moving when the engine 12 is being 
restarted, the running condition of the vehicle 11 is not unintendedly 
changed. Also, it normally takes a certain time period from when the 
engine 12 is stopped until when the engine 12 is restarted. Therefore, 
even if the relationship between the throttle opening TA and the gas pedal 
depression amount PA is changed after the normal state control is resumed, 
the driver will not be disturbed about the control of the gas pedal 35. 
A fourth embodiment of the present invention will now be described with 
reference to FIGS. 6 and 7. 
To avoid a redundant description, like or the some reference numerals are 
given to those components that are like or the same as the corresponding 
components of the first embodiment. 
FIG. 6 is a flowchart showing a throttle opening control routine according 
to the fourth embodiment. In steps having the same numerals as those in 
FIG. 4, the ECU 50 performs the same processes as in the first embodiment. 
The ECU 50 executes the routine of FIG. 6 with predetermined intervals 
after the engine 12 is started. 
If the condition of step 130 is not satisfied, the ECU 50 executes the 
processes of steps 160 to 190. After setting the abnormality flag XFAIL to 
zero at step 180 or after setting the flag XFAIL to one at step 190, the 
ECU 50 moves to step 200. At step 200, the ECU 50 resets a return counter 
value CFAIL to zero. 
If the condition at step 130 is satisfied, that is, if the abnormality flag 
XFAIL has already been set to one, the ECU 50 moves to step 136. At step 
136, the ECU judges whether a return determination flag XNORM is set to 
one. The return determination flag XNORM indicates whether a predetermined 
time period has elapsed after the return condition of step 140 was 
satisfied in the previous routine or earlier. If the condition of step 136 
is not satisfied, the ECU 50 moves to step 140. 
At step 140, the ECU 50 judges whether either the return condition (2-a) of 
the first embodiment or the return condition (2-b) of the second 
embodiment is satisfied. If the determination is positive, the ECU 50 
moves to step 210. At step 210, the ECU 50 sets the return determination 
flag XNORM to one. 
If the determination is positive at step 136, or after executing the 
process of step 210, the ECU 50 moves to step 220 in FIG. 7. In steps 220 
to 280, the ECU 50 gradually reduces the difference between an adjusted 
target opening TTA, which is used for controlling the valve 23, and a 
target opening TTAH. This process will hereafter be referred to as opening 
difference reduction. 
At step 220, the ECU 50 increments the return counter value CFAIL by one. 
The value of the return counter value CFAIL shows how long the return 
condition of step 140 has been satisfied. 
At step 230, the ECU 50 judges whether the return counter value CFAIL is 
greater than a determination value KFAIL. In this embodiment, the 
determination value KFAIL corresponds, for example, to three seconds. The 
return counter value CFAIL never exceeds the determination value KFAIL. If 
the condition of step 230 is not satisfied, the ECU 50 moves to step 260. 
At step 260, the ECU 50 computes the adjusted target opening TTA based on 
the following equation: 
EQU TTA=TTAH.times.(CFAIL/KFAIL) (1) 
As obvious in the equation (1), the adjusted target opening TTA increases 
as the return counter value CFAIL increases until TTA becomes equal to the 
target opening TTAH. 
At step 270, the ECU 50 controls the throttle valve 23 in accordance with 
the adjusted target opening TTA. As the process of step 270 is repeatedly 
executed, the adjusted target opening TTA is gradually increased. 
Accordingly, the throttle opening TA is gradually increased until it is 
equal to the target opening TTAH. 
At step 280, the ECU 50 judges whether the return determination flag XNORM 
is set to one. If the flag XNORM is set to one, the ECU 50 temporarily 
terminates the current routine. 
If the condition in step 230 is satisfied, that is, if the return counter 
value CFAIL is greater than the determination value KFAIL, the ECU 50 
moves to step 240. At step 240, the ECU 50 equalizes the return counter 
value CFAIL with the determination value KFAIL. Accordingly, the adjusted 
target opening TTA is set equal to the target opening TTAH at step 260. 
At step 250, the ECU 50 sets the return determination flag XNORM to zero. 
Therefore, after the ECU 50 executes the processes of steps 260 and 270, 
the determination is negative at step 280. The ECU 50 thus moves to step 
170 shown in FIG. 6. At step 170, the ECU 50 judges whether there is a 
malfunction in the electric component E. The ECU 50 then sets the value of 
the abnormality flag XFAIL either at step 180 or at step 190 based on the 
determination of step 170. Thereafter, the ECU 50 resets the return 
counter value CFAIL to zero. 
As described above, if the return condition is satisfied after an 
occurrence of malfunction of the electric component E, the ECU 50 does not 
immediately resume the normal state control, in which the throttle opening 
TA is equalized with a target opening TTA. Instead, the ECU 50 controls 
the throttle opening TA to gradually approach the target opening TTAH in 
stages as the return counter value CFAIL increases. 
Therefore, an abrupt change of the throttle opening TA, which would be 
caused by resumption of the normal state control of the valve 23, is 
prevented. This prevents a throttle opening TA corresponding to a certain 
pedal depression amount PA from being quickly and significantly changed 
when the normal state control is resumed. The driver is thus not disturbed 
about the feeling of the gas pedal 35 when the normal state control of the 
valve 23 is resumed. 
In this embodiment, the opening difference reduction is executed after at 
least one of the return conditions (2-a) and (2-b) is satisfied. 
Therefore, when the opening difference reduction is started, the selector 
lever of the automatic transmission 49 is in the neutral position or in 
the parking position, or the gas pedal depression amount PA and the 
vehicle speed SPD are both zero. Thus, starting the opening difference 
reduction during the malfunctioning state control of the throttle valve 23 
does not affect the running state of the vehicle. This also prevents the 
driver from being disturbed about the feeling of the gas pedal 35. 
A fifth embodiment of the present invention will now be described with 
reference to FIGS. 6 and 8. 
The differences from the first embodiment will mainly be discussed below, 
and like or the same reference numerals are given to those components that 
are like or the same as the corresponding components of the first 
embodiment. 
FIGS. 6 and 8 are flowcharts showing a throttle opening control routine 
according to the fifth embodiment. In steps having the same numerals as 
those in FIG. 7, the ECU 50 performs the same processes as in the first 
embodiment. 
If the condition at step 136 is satisfied, or after executing the process 
of step 210, the ECU 50 moves to step 221 of FIG. 1. At step 221, the ECU 
judges whether the gas pedal depression amount PA is zero. If the 
condition is not satisfied, that is, if the gas pedal 35 is being pressed 
by the driver, the ECU 50 moves to step 225. At step 225, the ECU 50 sets 
an opening change flag XOPEN, which will be discussed later, to one and 
moves to step 230. 
If the condition is satisfied at stop 221, that is, if the gas pedal 35 is 
not pressed at all, the ECU 50 moves to step 222. 
At step 222, the ECU 50 judges whether the opening change flag XOPEN is set 
to one. If the flag XOPEN is one, the gas pedal depression amount PA has 
been changed to zero in the current routine. If the condition go step 222 
is not satisfied, that is, if the pedal depression amount PA is 
continually zero in the previous and current routines, the ECU 50 moves to 
step 230. 
If the condition of step 222 is satisfied, the ECU 50 moves to step 223. At 
step 223, the ECU 50 sets the opening change flag XOPEN to zero. At step 
224, the ECU 50 increments the return counter value CFAIL by one and 
executes the processes of step 230 and the following steps. 
As described above, when the electric component E resumes controlling the 
throttle valve 23, the throttle opening TA is controlled to gradually 
approach a target opening TTA every time the gas pedal depression amount 
PA becomes zero, or every time the driver releases the gas pedal 35. 
Therefore, the gas pedal depression amount PA needs to be set to zero 
several times for resuming the normal state control of the throttle 
opening TA. That is, the driver has to repeatedly release the gas pedal 
35. Therefore, an abrupt change of the throttle opening TA is prevented. 
The driver thus is not disturbed by the feeling of the gas pedal 35 when 
the normal state control of the valve 23 is resumed. 
It should be apparent to those skilled in the art that the present 
invention may be embodied in many other specific forms without departing 
from the spirit or scope of the invention. Particularly, it should be 
understood that the invention may be embodied in the following forms. 
(1) In the first embodiment, the return condition is that the selector 
lever of the automatic transmission 49 is either in the neutral position 
or in the parking position. However, the return condition may be satisfied 
only when the selector lever is in the neutral position, or only when the 
selector lever is in the parking position. Also, one of the conditions 
(2-a) of the first embodiment and (2-b) of the second embodiment may be 
used as the return condition. 
(2) In the first to fifth embodiments, the electric component E is judged 
to be malfunctioning when at least one of the conditions (1-a) to (1-g) is 
not satisfied. However, a malfunction of the component E may be detected 
when two or more conditions (1-a) to (1-g) are not satisfied. 
(3) In the fourth and fifth embodiments, the opening difference reduction 
is performed when the return conditions (2-a) and (2-b) are both 
satisfied. However, even it the conditions (2-a) and (2-b) are not 
satisfied, the opening difference reduction may be performed, for example, 
with predetermined intervals. Also, the opening difference reduction may 
be performed every time the vehicle speed SPD becomes zero. Alternatively, 
the opening difference reduction may be performed when the brake pedal is 
pressed by a predetermined amount. 
(4) In the first to fifth embodiment, the throttle valve opening sensor 44 
and the gas pedal sensor 45 both include a pair of detectors. However, the 
sensors 44 and 45 may each employ a single detector. 
(5) In the fifth embodiment, the return counter value CFAIL is incremented 
every time the gas pedal depression amount PA becomes zero and the 
difference between the adjusted target opening TTAH and the target opening 
TTA is decreased, accordingly. However, the return counter value CFAIL may 
be incremented every time the vehicle speed SPD becomes zero. 
(6) In the fourth and fifth embodiments, the return counter value CFAIL is 
incremented by a constant amount. However, the amount by which the value 
CFAIL is incremented may vary in accordance with parameters indicating the 
running state of the engine 12, such as the engine speed NE and the intake 
pressure PM, and the vehicle speed SPD. 
(7) In the fourth embodiment, the throttle opening TA is gradually 
increased in stages in accordance with increase in the counter value CFAIL 
until TA matches the target opening TTAH. However, the throttle opening TA 
may be gradually changed with a constant increase rate until TA matches 
the target opening TTAH. Alternatively, the throttle opening TA may be 
changed with an increasing increase rate. 
(8) In the first to fifth embodiments, the electric motor 29 is used to 
operate the throttle valve 23. However, an actuator using fluid pressure 
may be used instead. 
(9) In the second embodiment, the return conditions are that the gas pedal 
depression amount PA is zero and the vehicle speed SPD is zero. However, 
the return condition may be satisfied when only the vehicle speed SPD is 
zero. Alternatively, the return condition may be satisfied when the gas 
pedal depression amount PA is zero and the selector lever of the automatic 
transmission 49 is in the neutral position or in the parking position. 
Therefore, the present examples and embodiments are to be considered as 
illustrative and not restrictive and the invention is not to be limited to 
the details given herein, but may be modified within the scope and 
equivalence of the appended claims.