Unit for controlling electronically controlled throttle valve

A control unit for detecting an opening of an accelerator and an opening of the throttle valve to operate the throttle valve via a motor, sets a commanded value of an opening of the throttle valve at each of first predetermined cycles in accordance with an of the accelerator. A first opening/closing velocity is set in accordance with the set commanded value, a present opening of the throttle valve is read at each of second cycles shorter than the first predetermined cycles, the motor is rotated to open/close the throttle valve to follow a first predicted opening of the throttle valve until the opening of the throttle valve is smaller than the commanded value by a predetermined quantity, and the motor is caused to open/close the throttle valve to follow a second predicted opening of the throttle valve which is smaller than the first predicted opening of the throttle valve after the cycle when the opening of the throttle valve has been made smaller than the commanded value by a predetermined quantity. As a result, high-speed response of the throttle valve and prevention of overshoot can be realized.

INCORPORATION BY REFERENCE
 The disclosure of Japanese Patent Applications No. HEI 10-226034 filed on
 Aug. 10, 1998 and No. HEI 10-341740 filed on Dec. 1, 1998, including the
 specification, drawings and abstracts thereof are incorporated herein by
 reference in their entirety.
 BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to a control unit, and more particularly to a
 control unit for an electronically controlled throttle valve which is
 capable of raising response speed of an electronically controlled throttle
 valve having a structure in which an acceleration pedal and the throttle
 valve are not mechanically connected to each other.
 2. Description of the Related Art
 Hitherto, control of the number of revolutions of an internal combustion
 engine mounted on a vehicle has been performed in accordance with an
 amount of depression of an acceleration pedal disposed in a driver's
 compartment adjacent to a foot of a driver. That is, internal combustion
 engines have generally incorporated a throttle valve disposed in a suction
 passage of the engine with the throttle valve connected to the
 acceleration pedal by a wire. When the acceleration pedal is depressed,
 the opening of the throttle valve is enlarged. Thus, an amount of air
 admitted into the internal combustion engine is enlarged, leading to an
 increased consumption of fuel. As a result, the number of revolutions of
 the internal combustion engine is enlarged.
 Recent advances with computers have lead to the increased use of
 electronically controlled internal combustion engines which optimally
 control revolution speed of the engine. Electronic control of the internal
 combustion engine, for example, control of an amount of fuel injection,
 control of an ignition timing, and control of a timing at which a
 suction/exhaust valve operates have been previously developed, and have
 been followed by the practical application of the electronic control of
 the throttle valve.
 The structure of an electronically controlled throttle valve unit is shown
 in FIG. 1. The electronically controlled throttle valve unit 20
 incorporates a throttle lever 16 connected to an acceleration pedal (not
 shown) by a wire; an accelerator opening sensor 15 contained in the
 throttle lever 16 for detecting an opening of an accelerator corresponding
 to an amount of depression of the accelerator pedal; an engine control
 unit (hereinafter called an "ECU") 10 to which the opening of the
 accelerator detected by the accelerator opening sensor 15 is input; a
 throttle motor 4 for opening/closing a throttle valve 3 disposed in a
 suction passage 2 of the internal combustion engine in accordance with an
 output of the ECU 10; a throttle opening sensor 5 for detecting an opening
 of the throttle valve 3; a lever 17 for withdrawal running; a return
 spring 18 for the throttle valve 3; and a relief spring 19 for the lever
 17 for withdrawal running. The throttle motor 4 has a built-in
 electromagnetic clutch.
 In the electronically controlled throttle valve unit 20 structured as
 described above, when the acceleration pedal is depressed in accordance
 with the intention of a driver, the amount of depression of the
 acceleration pedal is transmitted to the throttle lever 16 by the wire. As
 a result, the throttle lever 16 is rotated. The throttle lever 16 includes
 the accelerator opening sensor 15. In accordance with the angle of
 rotation of the throttle lever 16, the amount of depression of the
 acceleration pedal is detected. The amount of depression of the
 acceleration pedal detected by the accelerator opening sensor 15 is sent
 to the ECU 10. The ECU 10 determines the opening of the throttle valve 3
 in accordance with the detected amount of depression of the acceleration
 pedal so as to rotate the throttle motor 4. The opening of the throttle
 valve 3 is detected by the throttle opening sensor 5 so as to be fed back
 to the ECU 10. The throttle motor 4 must be a motor exhibiting quick
 response and small power consumption.
 To perform the above-mentioned control, a signal transmitted from the
 throttle opening sensor 5 for detecting the opening of the throttle valve
 3 is used. Moreover, a feedback control of the throttle motor 4 is
 performed by using proportion (P), integration (I) and differentiation (D)
 (hereinafter simply called "PID control") to eliminate deviation from the
 signal transmitted from the accelerator opening sensor 15.
 In recent years, electronic throttle apparatus have been suggested which
 are structured such that the wire between the acceleration pedal and the
 throttle valve 3 is eliminated. The foregoing electronic throttle
 apparatus incorporate a rotational-angle sensor provided for a support
 shaft of the acceleration pedal. As an alternative to this, a stroke
 sensor for the acceleration pedal is provided. The value detected by the
 sensor is directly input to the ECU 10.
 The ECU 10 determines the opening of the throttle valve 3 in response to a
 signal representing an opening of the acceleration pedal. Thus, the ECU 10
 directly outputs an operating signal to the throttle motor 4. The opening
 of the throttle valve 3 is detected by the throttle opening sensor 5 so as
 to be fed back to the ECU 10. Note that the throttle opening sensor 5 may
 be contained in the throttle motor 4.
 The control constants of the PID control including terms P, I and D have
 been fixed values determined by a tuning operation to satisfy
 specifications required for all of the running states of the system.
 Therefore, the conventional control unit for the electronically controlled
 throttle valve using the PID control cannot provide an optimum value for
 each running state of the engine. As a result, response and stability of
 the throttle valve 3 deteriorate.
 To improve response of the operation of the throttle valve with respect to
 the acceleration pedal, an attempt has been made to enlarge the gain in
 the PID control. The foregoing structure encounters another problem of
 causing overshoot at the time of acceleration and undershoot at the time
 of deceleration. To improve response of the operation of the throttle
 valve with respect to the acceleration pedal, a structure has been
 employed in which sampling cycles for detecting the opening of the
 throttle valve are shortened to quickly follow a target value (commanded
 value) in the PID control. If the sampling cycles are shortened to reduce
 the controlling intervals of the throttle motor 4, overshoot and
 undershoot may easily occur.
 Therefore, Japanese Patent Application Laid-Open No. HEI 8-326561 has been
 disclosed to overcome the problem of the overshoot and undershoot with
 respect to the target value of the opening of the throttle valve.
 According to the foregoing disclosure, a method has been suggested with
 which the PID control of the throttle valve is performed such that a state
 of the operation of the throttle valve is determined. If the determination
 is made that the throttle valve is being operated in a state in which the
 opening is larger than the target opening which is determined in
 accordance with the amount of depression of the acceleration pedal, it is
 determined that overshoot of the throttle valve has occurred. Thus, the
 gain (the differential term D) for use in the PID control is changed.
 If the gain is changed after the determination of the overshoot of the
 throttle valve as is suggested in Japanese Patent Application Laid-Open
 No. HEI 8-326561, the throttle valve has already been within the overshoot
 region. Therefore, there arises a problem of insufficient response to
 restore the throttle valve to a normal operation state.
 SUMMARY OF THE INVENTION
 Accordingly, an object of the present invention is to provide a control
 unit for an electronically controlled throttle valve for performing PID
 control capable of realizing both high-speed response of the
 electronically controlled throttle valve and prevention of overshoot by
 raising the velocity at which the throttle valve is opened/closed in
 accordance with a commanded value for the opening of the throttle valve
 and by monitoring the opening/closing velocity of the throttle valve to
 reduce the opening/closing velocity of the throttle valve after a moment
 at which the opening of the throttle valve has approached the opening
 based on the commanded value.
 To achieve the foregoing object, according to an aspect of the present
 invention, there is provided a control unit including an accelerator
 opening sensor for detecting an accelerator opening in accordance with an
 amount of depression of an acceleration pedal, a throttle-valve opening
 sensor for detecting an opening of a throttle valve disposed in a suction
 passage of an internal combustion engine, a motor for opening/closing the
 throttle valve in accordance with values detected by the accelerator
 opening sensor and the throttle-valve opening sensor, commanded-value
 setting means for setting a commanded value of the opening of the throttle
 valve in accordance with the accelerator value, first controlled-variable
 setting means for setting a first controlled variable of the throttle
 valve in accordance with the commanded value, second controlled-variable
 setting means for setting a second controlled variable in accordance with
 the first controlled variable when the difference between the present
 opening of the throttle valve and a previous opening of the throttle valve
 is smaller than a predetermined value, and controlled-variable output
 means for outputting the first and second controlled variables to the
 motor for opening the throttle valve until the opening reaches the
 commanded value of the opening of the throttle valve.

DESCRIPTION OF THE PREFERRED EMBODIMENT
 Referring to the drawings, embodiments of the present invention will now be
 described. Note that the same elements as those of the electronically
 controlled throttle valve unit 20 described with reference to FIG. 1 are
 given the same reference numerals.
 FIG. 2 schematically shows an electronically controlled fuel injection and
 multiple-cylinder internal combustion engine 1 incorporating the control
 unit for a throttle valve according to an embodiment of the present
 invention. Referring to FIG. 2, a suction passage 2 of the internal
 combustion engine 1 is provided with a throttle valve 3 disposed
 downstream of an air cleaner (not shown). A throttle motor 4 which is an
 actuator for operating the throttle valve 3 is disposed at an end of a
 shaft of the throttle valve 3. On the other hand, a throttle opening
 sensor 5 for detecting the opening of the throttle valve 3 is disposed at
 another end of the foregoing shaft. That is, the throttle valve 3
 according to this embodiment is an electronically controlled throttle
 which is opened/closed by the throttle motor 4.
 A surge tank 6 is disposed in the suction passage 2 at a position
 downstream of the throttle valve 3. A pressure sensor 7 for detecting the
 pressure of admitted air is disposed in the surge tank 6. Moreover, a fuel
 injection valve 8 for supplying pressurized fuel from a fuel supply system
 to a suction port is disposed at a position downstream of the surge tank
 6, the fuel injection valve 8 being provided for each cylinder. An output
 of the throttle opening sensor 5 and that of the pressure sensor 7 are
 supplied to an ECU (Engine Control Unit) 10 including a microcomputer.
 A water-temperature sensor 11 for detecting the temperature of cooling
 water is disposed in a cooling-water passage 9 of the cylinder block of
 the internal combustion engine 1. The water-temperature sensor 11
 generates an analog-voltage electric signal corresponding to the
 temperature of the cooling water. The exhaust-gas passage 12 is provided
 with a three way catalytic converter (not shown) for simultaneously
 purifying hazardous components which are HC, CO and NOx contained in
 exhaust gas. An O.sub.2 sensor 13 which is one of air-fuel ratio sensor is
 disposed in the exhaust-gas passage 12 at the position upstream of the
 catalytic converter. The O.sub.2 sensor 13 generates an electric signal to
 correspond to the density of an oxygen component contained in the exhaust
 gas. Outputs of the water-temperature sensor 11 and the O.sub.2 sensor 13
 are supplied to the ECU 10.
 The ECU 10 is furthermore supplied with a signal representing an amount of
 depression of the acceleration pedal (an accelerator opening signal)
 supplied from an accelerator opening sensor 15 joined to the accelerator
 pedal 14 and -arranged to detect the amount of depression of the
 accelerator. Moreover, the ECU 10 is supplied with engine speed Ne of the
 engine from a crank angle sensor joined to a distributor (not shown).
 The structure is arranged as described above. When a key switch (not shown)
 is switched on, the ECU 10 is energized so that a program is started.
 Thus, the ECU 10 extracts outputs from the foregoing sensors and controls
 the throttle motor 4 for opening/closing the throttle valve 3 and the fuel
 injection valve 8 or the other actuators. The ECU 10 incorporates an A/D
 converter for converting analog signals supplied from the various sensors
 into digital signals. Moreover, the ECU 10 incorporates an input/output
 interface 101 through which digital signals supplied from the various
 sensors and signals for operating the various actuators are input/output,
 a CPU 102 for performing a calculating process, memories, such as a ROM
 103 and a RAM 104, and a clock 105. The foregoing units are connected to
 one another through a bus 106. Since the structure of the ECU 10 has been
 already known, further description is omitted.
 When the signal representing the amount of depression of the acceleration
 pedal has been input to the ECU 10 from the accelerator opening sensor 15,
 the ECU 10 samples the signal representing the amount of depression of the
 acceleration pedal at predetermined cycles T, for example, cycles of 10
 ms, as shown in FIG. 3A. Then, the ECU 10 outputs sampled value .alpha. at
 time ta as commanded value .theta.CM of the opening of the throttle valve
 at time ta, as shown in FIG. 3B. Then, the ECU 10 similarly outputs the
 signal representing the amount of depression of the acceleration pedal and
 sampled at the predetermined cycles T such that the signal is output as
 commanded value .theta.CM=.beta. at time tb and commanded value
 .theta.CM=.gamma. at time tc.
 FIG. 4 is a block diagram showing functions of the ECU 10 shown in FIG. 2.
 When the signal representing the amount of depression of the acceleration
 pedal has been supplied to the ECU 10, a commanded-value setting function
 110 produces a commanded value at the predetermined time T. The commanded
 value is supplied to a PID control function 111 constituted by a
 differential operation function 111D, a proportional operation function
 111P and an integration operation function 111I. In accordance with the
 commanded value, the PID control function 111 calculates an
 opening/closing velocity of the throttle valve. Then, the PID control
 function 111 outputs a target value of the opening of the throttle valve
 which is determined by the opening/closing velocity of the throttle valve.
 The target value of the opening of the throttle valve is output to a duty
 output calculating function 112. The duty output calculating function 112
 calculates a duty ratio of an operating signal for the throttle motor in
 accordance with the target value of the opening of the throttle valve. The
 duty ratio of an operating signal for the throttle motor is output to the
 throttle motor 4. Thus, the throttle motor 4 is rotated so that the
 opening of the throttle valve is changed. The opening of the throttle
 valve is detected by the throttle opening sensor 5. A detected value is
 fed back to the PID control function 111.
 The system for controlling the throttle valve has the above-mentioned
 functions. The control system according to the present invention has an
 acceleration/deceleration prediction calculating function 113 added
 thereto. The acceleration/deceleration prediction calculating function 113
 extracts the output of the duty output calculating function 112 and
 controls the output of the duty output calculating function 112 by feeding
 back a predetermined signal to an input portion of the duty output
 calculating function 112. The opening of the throttle valve detected by
 the throttle opening sensor 5 is also input to the
 acceleration/deceleration prediction calculating function 113.
 A first embodiment of the control according to the present invention for
 use in the control unit having the above-mentioned structure shown in FIG.
 4 will now be described with reference to a flow chart shown in FIG. 5.
 The procedure shown in the foregoing flow chart is performed at individual
 sampling cycles Ts shorter than the foregoing sampling cycles T. It is
 assumed that m is a natural number, T=mTs.
 In step 501, it is determined whether or not the present time is the
 sampling period T. If the present time is the sampling period T, the
 operation proceeds to step 502 where a present opening (the amount of
 depression of the acceleration pedal) detected by the accelerator opening
 sensor 15 is read as shown in FIGS. 3A and 3B. The read opening is made to
 be a present commanded value .theta.CM of the opening of the throttle
 valve. In step 503, first opening/closing velocity V1 of the throttle
 valve is calculated in accordance with the magnitude of the commanded
 value .theta.CM. Then, the operation proceeds to step 504.
 The first opening/closing velocity V1 indicates an upper limit for a
 follow-up velocity of the opening of the throttle valve with respect to
 the commanded value .theta.CM. The follow-up velocity of the opening of
 the throttle valve with respect to the commanded value .theta.CM is
 guarded with the first opening/closing velocity V1. The first
 opening/closing velocity V1 may be determined in accordance with the
 magnitude of the commanded value .theta.CM at the time at which the first
 opening/closing velocity V1 is calculated by forming the same into a map
 which is previously stored in the ROM 103. Also the first opening/closing
 velocity V1 of the throttle valve can be obtained by present control. That
 is, also the first opening/closing velocity V1 of the throttle valve can
 be obtained by producing a state equation by using parameters including
 the commanded value .theta.CM, the amount of depression of the accelerator
 pedal, the voltage of a battery and the temperature detected at the time
 at which the first opening/closing velocity V1 is calculated.
 If it is determined in step 501 that the present time t1 is not the
 sampling period T, steps 502 and 503 are not performed. In this case, the
 operation proceeds to step 504.
 In step 504, the opening .theta.th of the throttle valve 3 is read in
 accordance with an output denoting the result of detection performed by
 the throttle opening sensor 5. In step 505, predicted opening .theta.e1 of
 the throttle valve after a lapse of predetermined time Ts (after next
 sampling cycle Ts) in accordance with the first opening/closing velocity
 V1 of the throttle valve calculated in step 503 and the present opening
 .theta.th of the throttle valve 3. The predicted opening .theta.e1 of the
 throttle valve is a quantity which is expressed as the difference from the
 present opening .theta.th of the throttle valve.
 In step 506, an amount of rotations of the throttle motor 4 for operating
 the throttle valve 3 is calculated as a drive duty ratio DD1 to correspond
 to the predicted opening .theta.e1 of the throttle valve calculated in
 step 505. The drive duty ratio DD1 can be calculated in accordance with
 the map made to correspond to the predicted opening .theta.e1 of the
 throttle valve.
 Examples of the foregoing map are shown in FIGS. 6 and 7. FIG. 6 shows an
 example of a map having the X-axis standing for predicted opening (the
 velocity) and the Y-axis standing for drive duty ratios DD1. In accordance
 with the foregoing map, the drive duty ratio DD1 corresponding to the
 predicted opening .theta.e1 can be obtained. FIG. 7 shows an example of a
 map having the X-axis standing for the positions of the throttle valve,
 the Y-axis standing for the predicted openings of the throttle valve and
 the Z-axis standing for the drive duty ratios DD1. The map shown in FIG. 7
 enables the value of the drive duty ratio DD1 corresponding to the
 predicted opening .theta.e1 to be obtained in consideration of the present
 position of the throttle valve (the opening of the throttle valve).
 Therefore, a further accurate drive duty ratio DD1 can be obtained.
 In this embodiment, the foregoing control is performed until the opening
 .theta.th is enlarged to a predetermined opening near the commanded value
 .theta.CM of the opening of the throttle valve 3. The predetermined
 opening varies depending on the performance of the engine. The
 predetermined opening is required to be, for example, about 85% of the
 commanded value .theta.CM of the opening of the throttle valve. Then, the
 description will be performed such that the predetermined opening is 85%
 of the commanded value .theta.CM of the opening of the throttle valve.
 In step 507, it is determined whether or not the opening .theta.th of the
 throttle valve 3 has been enlarged to the predetermined opening near the
 commanded value .theta.CM of the opening of the throttle valve, that is,
 it is determined whether or not the opening .theta.th of the throttle
 valve 3 has been enlarged to 85% of the commanded value .theta.CM. If
 .theta.th&lt;.theta.CM.times.0.85 in step 507, the drive duty ratio DD1
 obtained by the procedure in step 502 to step 506 is as it is used to
 rotate the throttle motor 4. Therefore, if .theta.th&lt;.theta.CM.times.0.85
 in step 507, the operation proceeds to step 508 where a flag n, to be
 described later, is made to be 0. Then in step 16, the drive duty ratio
 DD1 calculated in step 5 is output as the duty ratio for rotating the
 throttle motor 4. Thus, the foregoing routine is completed.
 If .theta.th.gtoreq..theta.CM.times.0.85 in step 507, the operation
 proceeds to step 509. In step 509, it is determined whether or not
 .theta.th.gtoreq..theta.CM.times.0.85 has been first satisfied in step 507
 in accordance with the value of the flag. That is, if
 .theta.th.gtoreq..theta.CM.times.0.85 has been first satisfied in step
 507, the value of the flag n is zero. Therefore, the process in steps 510
 and 511 are performed. When the value of the flag n is zero, the operation
 proceeds to step 510 where second opening/closing velocity V2 of the
 throttle valve is calculated in accordance with the first opening/closing
 velocity V1 of the throttle valve. The second opening/closing velocity V2
 of the throttle valve is smaller than the first opening/closing velocity
 V1 of the throttle valve. The second opening/closing velocity V2 can be
 calculated by using the map as shown in FIG. 8 and previously set in
 accordance with the first opening/closing velocity V1 of the throttle
 valve. The map shown in FIG. 8 is required to be corrected in accordance
 with the state of the throttle motor, the voltage of the battery mounted
 on the engine or the atmospheric temperature.
 After the second opening/closing velocity V2 of the throttle valve has been
 calculated in step 510, the operation proceeds to step 511 where the value
 of the flag n is made to be 1. Then the operation proceeds to step 512.
 When the operation proceeds to step 509 afterwards, the value of the flag
 n has been made to be 1. Therefore, the processes in steps 510 and 511 are
 not performed. In this case, the operation proceeds to step 512. As
 described above, the flag n is provided for causing the second
 opening/closing velocity V2 of the throttle valve to be calculated in step
 510 only when .theta.th.gtoreq..theta.CM.times.0.85 is first satisfied in
 step 507.
 In step 512, predicted opening .theta.e2 of the throttle valve after a
 lapse of the predetermined time Ts is calculated in accordance with the
 second opening/closing velocity V2 of the throttle valve calculated in
 step 510 and the present opening .theta.th of the throttle valve 3 read in
 step 504.
 In step 513, difference .theta.thdf between the predicted opening .theta.e1
 of the throttle valve calculated in step 505 and the predicted opening
 .theta.e2 of the throttle valve calculated in step 512 is calculated. In
 step 514, change DD.DELTA. of the drive duty ratio DD1 of the throttle
 motor 4 which operates the throttle valve 3 is calculated to correspond to
 the difference .theta.thdf. The change DD.DELTA. of the drive duty ratio
 can be calculated by directly using the map caused to correspond to the
 predicted opening .theta.e1 of the throttle valve.
 In step 515, the drive duty ratio DD1 of the throttle valve calculated in
 step 506 is corrected with the change DD.DELTA. of the drive duty ratio
 calculated in step 514. After the process in step 515 has been completed,
 the operation proceeds to step 516 where the corrected drive duty ratio
 DD1 of the throttle valve is output as the drive duty ratio of the
 throttle motor 4. Thus, the foregoing routine is completed.
 Therefore, after .theta.th.gtoreq..theta.CM.times.0.85 has been satisfied
 in step 507, the drive duty ratio DD1 which is output in step 516 is the
 value obtained in step 515 by correcting the drive duty ratio DD1 of the
 throttle motor 4 calculated in step 506. The corrected drive duty ratio
 DD1 is used to rotate the throttle motor 4.
 FIG. 9 is a time chart for use when the time t1 corresponds to the
 calculating cycles of the commanded value .theta.CM and showing change in
 the commanded value .theta.CM, the opening of the throttle valve
 (predicted openings .theta.e1 and .theta.e2) and the drive duty ratio DD1
 of the throttle motor with time. It is assumed that the opening .theta.th
 of the throttle valve is no and the commanded value .theta.CM calculated
 in step 502 is 5.degree..
 Under the foregoing conditions, the first opening/closing velocity V1 of
 the throttle valve is calculated in accordance with the value of the
 commanded value .theta.CM which is 5.degree. (step 503). Then the value
 5.degree. as the present opening .theta.th of the throttle valve is read
 (step 504). Then, the predicted opening .theta.e1 of the throttle valve
 after a lapse of the sampling cycle Ts is calculated (step 505). Note that
 the predicted opening of the throttle valve after a lapse of the sampling
 cycle Ts is made to be F.
 When the predicted opening of the throttle valve after a lapse of the
 sampling cycle Ts has been calculated as F, the corresponding drive duty
 ratio DD1 of the throttle motor is calculated (step 806). Thus, the
 throttle motor is duty-rotated with the foregoing drive duty ratio DD1
 (step 516).
 The duty rotation of the throttle motor is continued from time t1 to time
 t2 for period T1. When the predicted opening .theta.e1 of the throttle
 valve has been changed to F, A, B, C and E during the period T1 as shown
 in the graph, the drive duty ratio DD1 of the throttle motor is
 accordingly changed to F', A', B', C' and E'. The control in the period T1
 is the control using the PID control.
 If the opening .theta.th of the throttle valve has been enlarged to 85% of
 the commanded value .theta.CM at time t2, the second opening/closing
 velocity V2 of the throttle valve is, at time t2, calculated to correspond
 to the first opening/closing velocity V1 of the throttle valve (step 510).
 Then, the predicted opening .theta.e2 of the throttle valve after a lapse
 of sampling cycle Ts is calculated (step 512). Note that the predicted
 opening .theta.e1 of the throttle valve after a lapse of sampling cycle Ts
 is made to be D" and the predicted opening .theta.e2 of the throttle valve
 is made to be D.
 When the opening .theta.th of the throttle valve has been enlarged to 85%
 of the commanded value .theta.CM, both of D" of the predicted opening
 .theta.e1 corresponding to the first opening/closing velocity V1 of the
 throttle valve and D of the predicted opening .theta.e2 are calculated.
 Thus, the difference .theta.thdf between the two values is calculated
 (step 513). Then the change DD.DELTA. of the duty ratio corresponding to
 the difference .theta.thdf is calculated (step 514). Thus, the drive duty
 ratio DD1 of the throttle motor 4 is corrected with the change DD.DELTA.
 of the duty ratio (step 515). Then the throttle motor is rotated with the
 corrected drive duty ratio DD1 in a period of T2 until time t3 at which
 the opening .theta.th of the throttle valve coincides with the commanded
 value .theta.CM. The period T2 is the period in which an
 acceleration/deceleration prediction calculation is performed in the PID
 control according to the present invention.
 The control for opening the throttle valve has been described. When control
 is performed such that the throttle valve is closed, the sign of the
 magnitude of each of the commanded value .theta.CM, the opening (predicted
 openings .theta.e1 and .theta.e2) of the throttle valve and the drive duty
 ratio DD1 of the throttle motor is made to be negative. Therefore, the
 other portions are the same. Thus, the foregoing control is omitted from
 description.
 In the above-mentioned example, when the opening .theta.th of the throttle
 valve has been enlarged to 85% of the commanded value .theta.CM, the
 opening/closing velocity of the throttle valve is changed from the first
 opening/closing velocity V1 to the second opening/closing velocity V2
 which is lower than the first opening/closing velocity V1. The change from
 the first opening/closing velocity V1 to the second opening/closing
 velocity V2 is not limited at the moment when the opening .theta.th of the
 throttle valve has been enlarged to 85% of the commanded value .theta.CM.
 The timing may arbitrarily be selected in accordance with the performance
 of the engine. The change may be performed when the opening .theta.th of
 the throttle valve is made to be full close or near full open.
 As described with reference to FIG. 9, according to the present invention,
 the predicted openings .theta.e1 and .theta.e2 of the throttle valve can
 appropriately be determined with respect to the commanded value .theta.CM
 of the opening of the throttle valve as indicated with solid line RT.
 Moreover, the drive duty ratio DD1 of the throttle motor can appropriately
 be determined as indicated with solid line RD. Therefore, the throttle
 valve can smoothly be operated without causing overshoot and undershoot.
 On the other hand, the conventional control encounters the fact that the
 predicted opening .theta.e1 of the throttle valve is raised with respect
 to the commanded value .theta.CM of the opening of the throttle valve even
 after time t2 as indicated with an alternate long and two short dashes
 line UT. Therefore, also the drive duty ratio DD1 of the throttle valve is
 raised as indicated with an alternate long and two short dash line UD. As
 a result, overshoot and undershoot of the throttle valve take place.
 The example shown in FIG. 9 is structured such that the gain of the PID
 control is appropriately determined. Another example is shown in FIG. 10
 in which the gain of the PID control is enlarged to cause the predicted
 opening .theta.e1 of the throttle valve to always be guarded with the
 first opening/closing velocity V1. Also in the foregoing case, the
 predicted openings .theta.e1 and .theta.e2 of the throttle valve can
 appropriately be determined with respect to the commanded value .theta.CM
 of the throttle valve as indicated with the solid line RT. Moreover, the
 drive duty ratio DD1 of the throttle motor can appropriately be determined
 as indicated with the solid line RD. Therefore, the throttle valve can
 smoothly be rotated without causing overshoot and undershoot.
 The first and second opening/closing velocities V1 and V2 may be provided
 with allowances as indicated with dashed lines V1a, V1b and V2a, V2b shown
 in FIG. 10.
 In the foregoing embodiment, even after the opening of the throttle valve
 has been enlarged to 85% of the commanded value .theta.CM, also the
 predicted opening .theta.e1 of the throttle valve corresponding to the
 first opening/closing velocity V1 of the throttle valve is calculated.
 Then the difference .theta.thdf between the predicted opening .theta.e2
 corresponding to the second opening/closing velocity V2 of the throttle
 valve and the predicted opening .theta.e1 is calculated. The difference
 .theta.thdf between the predicted opening .theta.e2 of the throttle valve
 corresponding the second opening/closing velocity V2 of the throttle valve
 and the predicted opening .theta.e1 of the throttle valve is calculated.
 Then the change DD.DELTA. of the duty ratio corresponding to the
 difference .theta.thdf is calculated. The change DD.DELTA. of the duty
 ratio of the throttle motor which can be obtained from the predicted
 opening .theta.e1 of the throttle valve corresponding to the first
 opening/closing velocity V1 of the throttle valve is corrected with the
 change DD.DELTA.. The throttle motor, thus, is rotated.
 After the opening .theta.th of the throttle valve has been enlarged to 85%
 of the commanded value .theta.CM, the drive duty ratio DD1 of the throttle
 motor may directly be calculated from the predicted opening .theta.e2 of
 the throttle valve of the throttle valve corresponding to the second
 opening/closing velocity V2 of the throttle valve so as to rotate the
 throttle motor. FIG. 11 is a flow chart of a second embodiment of the
 present invention based on the foregoing control procedure.
 The control procedure shown in FIG. 11 is similar to the control procedure
 shown in FIG. 5 except for a portion. The similar portions are given the
 same step numbers to those shown in FIG. 5 and the description thereof
 will be omitted.
 Steps 501 to 505 are the same as those of the procedure shown in FIG. 5. In
 step 501, it is determined whether or not the present time is sampling
 cycle T. In step 502, the commanded value .theta.CM of the opening of the
 throttle valve is calculated in accordance with the present amount of
 depression of the acceleration pedal. In step 503, the first
 opening/closing velocity V1 is calculated. In step 504, the present
 opening .theta.th of the throttle valve 3 is read. In step 505, predicted
 opening .theta.e1 of the throttle valve after a lapse of a predetermined
 time (sampling cycle) Ts is calculated.
 In the control shown in FIG. 5, the drive duty ratio DD1 of the throttle
 motor 4 corresponding to the predicted opening .theta.e1 of the throttle
 valve is calculated in step 506. In this embodiment, step 507 is performed
 after step 505 has been completed so that it is determined whether or not
 the opening .theta.th of the throttle valve 3 is about 85% of the
 commanded value .theta.CM of the opening of the throttle valve.
 If .theta.th&lt;.theta.CM.times.0.85 in step 507, the flag n is made to be
 zero in step 508. Then, step 601 corresponding to step 506 in the control
 shown in FIG. 5 is performed. That is, in step 601, the drive duty ratio
 DD1 corresponding to the predicted opening .theta.e1 is calculated. In
 step 516, the drive duty ratio DD1 calculated in step 601 is output as the
 drive duty ratio of the throttle motor 4. Thus, the foregoing routine is
 completed.
 The procedure which is performed from steps 509 to 512 when
 .theta.th.gtoreq..theta.CM.times.0.85 in step 507 are the same as those
 described in the procedure shown in FIG. 5. In step 509, it is determined
 whether or not .theta.th.gtoreq..theta.CM.times.0.85 has been first
 satisfied in step 507. In step 510, the second opening/closing velocity V2
 of the throttle valve is calculated in accordance with the first
 opening/closing velocity V1 of the throttle valve. In step 511, the value
 of the flag n is made to be 1. Instep 512 the predicted opening .theta.e2
 of the throttle valve after a lapse of a predetermined time (sampling
 cycle) Ts is calculated.
 In step 602, the drive duty ratio DD1 of the throttle motor corresponding
 to the predicted opening .theta.e2 is calculated. The operation proceeds
 to step 516 where the drive duty ratio DD1 of the throttle valve is output
 as the drive duty ratio of the throttle motor 4. Thus, the foregoing
 routine is completed.
 In this embodiment, after .theta.th.gtoreq..theta.CM.times.0.85 has been
 satisfied in step 507, the drive duty ratio DD1 output in step 516 is the
 drive duty ratio DD1 of the throttle motor 4 corresponding to the
 predicted opening .theta.e2 of the throttle valve calculated in step 602.
 The foregoing value is the same as the value of the drive duty ratio DD1
 corrected in step 515 in the control showing FIG. 5. Therefore, also this
 embodiment causes the throttle motor to be rotated similar to the control
 shown in FIG. 5.
 As described above, according to the present invention, control of the
 operation of the throttle valve is performed while predicting the drive
 duty ratio of the throttle motor. Therefore, prediction of the time taken
 for the throttle valve to reach a commanded value after the commanded
 value has been changed can be performed. As a result, the air fuel ratio
 can accurately be controlled. Therefore, emission of the engine can be
 reduced. Hitherto, the operation of the throttle valve cannot be detected
 when the engine side controls the air fuel ratio. The present invention
 enables the operation of the throttle valve to somewhat detected.
 Therefore, an amount of admitted air can be detected in accordance with
 the opening of the throttle valve after a lapse of a predetermined time.
 Therefore, corresponding fuel injection can be performed. As a result, the
 emission of the engine can be improved.
 The electronically controlled throttle valve unit 30 is arranged to prevent
 stall of the engine when control has failed and maintain an amount of air
 required for the engine. To achieve this, a state in which the throttle
 valve 3 is opened by a predetermined opening is maintained even after the
 accelerator pedal 14 has been returned. The foregoing opening of the
 throttle valve 3 is called the opener opening. The foregoing opening is
 usually set by an opener opening setting mechanism having springs for
 urging the throttle valve 3 in the opening direction and the closing
 direction, respectively.
 FIG. 12A shows an example of the opener opening setting mechanism 40 of the
 electronically controlled throttle valve unit 30 from which an accelerator
 cable disposed between the accelerator pedal 14 and the throttle valve 3
 has been omitted. The opener opening setting mechanism 40 urges the
 throttle valve 3 in the opening direction and the closing direction. FIGS.
 12B to 12D show the operation of the opener opening setting mechanism 40.
 Note that the throttle opening sensor is omitted from FIG. 12A.
 As shown in FIG. 12A, the throttle motor 4 for rotating a rotational shaft
 23 of the throttle valve 3 provided for the suction passage 2 is disposed
 at the end of the rotational shaft 23. A flange 22 is secured to another
 end of the rotational shaft 23. A first movable member 31 is provided for
 a predetermined position of the outer surface of the flange 22. A first
 spring 41 is arranged between the first movable member 31 and a throttle
 body (not shown) of the electronically controlled throttle valve unit 30.
 The first spring 41 urges the first movable member 31 in the direction in
 which the throttle valve 3 is opened.
 A movable ring 25 permitted to rotate around the rotational shaft 23 is fit
 to the rotational shaft 23 adjacent to the flange 22. A second movable
 member 32 arranged to be engaged to the first movable member 31 owning to
 the rotation of the movable ring 25 is provided for the outer surface of
 the movable ring 25. A second spring 42 is arranged between the second
 movable member 32 and the throttle body (not shown) of the electronically
 controlled throttle valve unit 30. The second spring 42 urges the second
 movable member 32 in the direction in which the throttle valve 3 is
 opened. In this embodiment, the urging force of the second spring 42 is
 set to be larger than that of the first spring 41.
 In addition to the foregoing structure, a stopper 26 for stopping the
 rotation of the second spring 42 is provided for the throttle body. The
 stopper 26 prevents exertion of the urging force of the second spring 42
 on the throttle valve 3, the opening of which is smaller than the opener
 opening. The stopper 26 does not exert the influence on the operation of
 the first movable member 31.
 The position of the flange 22 of the first movable member 31 and the
 relationship between the position of the second movable member 32 and the
 stopper 26 will now be described with reference to FIG. 12C. FIG. 12C
 shows the state in which the throttle valve 3 is opened at the opener
 opening. At this time, the second movable member 32 urged by the second
 spring 42 to rotate the throttle valve 3 in the opening direction is
 brought into contact with the stopper 26. Thus, the rotation of the second
 movable member 32 is interrupted. If the rotating force of a throttle
 motor (not shown) is not added to the rotational shaft 23 of the throttle
 valve in the foregoing state, the first movable member 31 is pulled by the
 first spring 41 so as to be brought into contact with the second movable
 member 32. As described above, the urging force of the first spring 41 is
 smaller than that of the second spring 42. Therefore, the throttle valve 3
 maintains the opener opening in the state in which the rotating force of
 the throttle motor is not exerted on the rotational shaft 23.
 FIG. 12B shows the state in which the throttle valve 3 has completely
 closed the suction passage 2.
 To close the throttle valve 3 from the opener opening to the completely
 closed state, the throttle motor is required to be rotated to exert
 rotating force larger than urging force F1 of the first spring 41 on the
 rotational shaft 23. Note a stopper (not shown) provided individually
 stops the rotation of the throttle valve 3 at the completely closed state.
 Therefore, the opening of the throttle valve 3 is not made to be a
 negative opening.
 FIG. 12D shows the state in which the throttle valve 3 has been opened at a
 predetermined opening which is larger than the opener opening. Both of the
 urging force F1 in a direction in which the throttle valve 3 is opened by
 the first spring 41 and urging force F2 in the direction in which the
 throttle valve 3 is opened by the second spring 42 are exerted on the
 first movable member 31 when the opening of the throttle valve 3 is larger
 than the opener opening. As described above, the urging force F1 of the
 first spring 41 is smaller than the urging force F2 of the second spring
 42. Therefore, urging force (F2-F1) obtained by subtracting the urging
 force F1 of the first spring 41 from the urging force F2 of the second
 spring 42 is exerted on the first movable member 31. That is, urging force
 (F2-F1) in the direction in which the throttle valve 3 is closed is
 exerted on the first movable member 31. To enlarge the opening of the
 throttle valve 3, rotating force larger than the urging force (F2-F1) may
 be exerted from the throttle motor to the rotational shaft 23.
 A case will now be described in which the electronically controlled
 throttle valve unit from which the accelerator cable arranged between the
 acceleration pedal and the throttle valve has been omitted is provided
 with the foregoing opener opening setting mechanism. When the throttle
 valve, which is completely closed, is operated in the direction in which
 the throttle valve is opened, the spring constant which acts on the
 rotational shaft of the throttle valve is changed in the vicinity of the
 opener opening at which the two springs are balanced. Therefore, the
 rotating force of the throttle motor for operating the throttle valve is
 changed. As a result, the throttle valve cannot smoothly be operated in
 the vicinity of the opener opening.
 A case will now be considered in which a command value for opening the
 throttle valve for a predetermined angular degree has been output from the
 unit for controlling the electronically controlled throttle valve in a
 state in which the throttle valve is completely closed as shown in FIG.
 13. In the foregoing case, the opening of the throttle valve stagnates for
 a certain period of time in the vicinity of the opener opening. Therefore,
 the throttle valve cannot smoothly be operated. Also in a case where the
 throttle valve is controlled from the opening position to the closing
 position across the opener opening, the throttle valve cannot smoothly be
 operated.
 A portion of the throttle motors for operating the electrically controlled
 throttle valve is able to uniformly generate torque over the full
 operation range of the engine. A portion of the throttle motors cannot
 perform the above-mentioned operation. When the motor which is capable of
 uniformly generating torque over the full operation range of the engine is
 adapted to the electrically controlled throttle valve, the torque for
 operating the throttle valve is sometimes insufficient owning to the
 environment for the operation. Therefore, the throttle valve cannot
 sometimes be operated in a smooth manner even at an angle except for the
 angle in the vicinity of the opener opening.
 Accordingly, the next embodiment is arranged to be capable of smoothly
 opening/closing the throttle valve even if the throttle valve is operated
 in the opening or closing direction across the opener opening or if the
 throttle valve cannot smoothly be operated at an opening except for the
 opener opening.
 This embodiment is structured such that the opener opening setting
 mechanism 40 (not shown) for setting the opening of the throttle valve 3
 is added to the structure shown in FIG. 2, which is disposed at the end of
 the rotational shaft of the throttle valve 3.
 FIG. 14 is a block diagram showing the functions of the ECU 10 for
 realizing a third embodiment. When the signal representing the amount of
 depression of the acceleration pedal has been input to the ECU 10, the
 commanded-value setting function 110 produces a commanded value at each
 predetermined time T, as described above. The commanded value is supplied
 to the PID control function 111 incorporating the differential operation
 function 111D, the proportional operation function 111P and the
 integration operation function 111I. In accordance with the foregoing
 commanded value, the PID control function 111 calculates the
 opening/closing velocity of the throttle valve. Moreover, the PID control
 function 111 outputs a target value of the opening of the throttle valve
 which is determined by the opening/closing velocity of the throttle valve.
 The target value of the opening of the throttle valve is supplied to the
 duty output calculating function 112. The duty output calculating function
 112 calculates a duty ratio of an operating signal for the throttle motor
 in accordance with the target value of the opening of the throttle valve.
 The duty ratio of the operating signal for the throttle motor 4 is output
 to the throttle motor 4. Thus, the throttle motor 4 is rotated so that the
 opening of the throttle valve is changed. The opening of the throttle
 valve is detected by the throttle opening sensor 5. The sign of a value
 detected by the throttle opening sensor 5 is inverted, and then added to
 the commanded value by an adding function Al so as to be fed back to the
 PID control function 111.
 The corresponding system for the usual throttle valve has the foregoing
 functions. In this embodiment, the foregoing control system further
 incorporates a function (a differentiating function) 113 for calculating
 the movement velocity of the throttle valve, two switches 114 and 115
 which are switched on/off by the function 113 for calculating the movement
 velocity of the throttle valve, a function 116 for calculating a predicted
 correcting term of the proportional operation, a function 117 for
 calculating a predicted correction term of the integration operation, and
 addition functions A2 and A3 for adding predicted correction terms of the
 predicted correction term of the proportional operation and the predicted
 correction term of the integration operation. The function 113 for
 calculating the movement velocity of the throttle valve detects the
 movement velocity of the throttle valve in accordance with the value
 detected by the throttle opening sensor 5 in a unit time. When the
 movement velocity of the throttle valve is lower than a predetermined
 value, the function 113 for calculating the movement velocity of the
 throttle valve switches the switches 114, 115 on. The function 116 for
 calculating a predicted correction term of the proportional operation and
 the function 117 for calculating a predicted correction term of the
 integration operation calculate the proportional operation and the
 integration operation, respectively, in accordance with a value detected
 by the throttle opening sensor 5. The predicted correction term calculated
 by the function 116 for calculating a predicted correction term of the
 proportional operation is, through the switch 114, output to the addition
 function A2 disposed between the proportional operation function 111P and
 the duty output calculating function 112. The predicted correction term
 calculated by the function 117 for calculating a predicted correction term
 of the integration operation is, through the switch 115, output to the
 addition function A3 disposed between the integration operation function
 111I and the duty output calculating function 112.
 Note that the two switches 114 and 115 are not mechanical switches and the
 foregoing switches are flags for operating the predicted correction terms
 116 and 117.
 A case of the unit for controlling the electronically controlled throttle
 valve structured as shown in FIG. 14 will now be considered. This case is
 the case in which the opening/closing velocity of the throttle valve is
 set and the opening of the throttle valve is caused to follow up the set
 opening after a commanded value of a predetermined opening, for example,
 an opening of 5.degree. is output. The relationship between the opening of
 the throttle valve and an actual value detected by the throttle opening
 sensor (expressed as throttle sensor in the drawing) will now be described
 in the case were the throttle valve has smoothly followed the
 opening/closing velocity of the throttle valve. The opening/closing
 velocity of the throttle valve with respect to the commanded value is
 sometimes the same until the opening of the throttle valve reaches the
 commanded value. In some cases, the foregoing opening/closing velocity is
 changed before the opening of the throttle valve reaches the commanded
 value.
 FIG. 15A shows the case in which the opening/closing velocity of the
 throttle valve with respect to the commanded value is constant until the
 opening of the throttle valve reaches the commanded value. When the
 commanded value has been set to the opening of 5.degree., the
 opening/closing velocity of a predetermined throttle valve is set as
 indicated with a thick line. Thus, the throttle valve is operated to
 follow up the opening/closing velocity at t. At this time, the value of
 the throttle sensor is read at each time Ts. The foregoing case is the
 case in which the throttle valve has smoothly followed up the
 opening/closing velocity of the throttle valve. Therefore, output values
 of the throttle sensor follow the opening/closing velocity of the throttle
 valve and, therefore, the values are changed stepwise. In the foregoing
 case, an allowable range indicated with dashed lines is provided for the
 opening/closing velocity of the throttle valve. If the output value of the
 throttle sensor is deviated from the foregoing range, the predicted
 correction terms 116 and 117 shown in FIG. 14 are operated.
 FIG. 15B shows the case in which a plurality of opening/closing velocities
 of the throttle valve with respect to a commanded value exist until the
 opening of the throttle valve reaches the commanded value. When the
 commanded value has been set to the opening of 5.degree., a region for
 accelerating the throttle valve which is 95% of 5.degree. and a region for
 decelerating the throttle valve which is 95% to 100% are set. As indicated
 with a thick line, a first opening/closing velocity of the throttle valve
 is set in the acceleration region. In the deceleration region, a second
 opening/closing velocity which is lower than the first opening/closing
 velocity is set. The throttle valve is operated to follow the first and
 second opening/closing velocity. At this time, the value of the throttle
 sensor is read at each time Ts. The foregoing case is a case in which the
 throttle valve has smoothly followed the opening/closing velocity of the
 throttle valve. Therefore, the output value from the throttle sensor
 follows the first and second opening/closing velocities and, therefore,
 the value is changed stepwise. Also in the foregoing case, allowable
 ranges for the output value from the throttle sensor indicated with dashed
 lines are provided for the first and second opening/closing velocities.
 Therefore, also in the foregoing case, if the output value from the
 throttle sensor is deviated from the foregoing ranges, the predicted
 correction terms 116 and 117 shown in FIG. 14 are operated.
 After the output value of the throttle sensor has temporarily been deviated
 from the foregoing range, the predicted correction terms 116 and 117 shown
 in FIG. 14 are operated when the deviation between the previous output of
 the throttle sensor and the present output is smaller than a reference
 value. The reference value is required to be half of the foregoing
 allowable range. When the deviation between the previous output of the
 throttle sensor and the present output is larger than the reference value
 after the output vale of the throttle sensor has temporarily be deviated
 from the foregoing range, the operations of the predicted correction terms
 116 and 117 shown in FIG. 14 are required to instantaneously stopped or
 gradually moderated.
 FIG. 16 shows the case in which the operations of the predicted correction
 terms 116 and 117 shown in FIG. 14 which are performed when the output
 value of the throttle sensor has been deviated from the allowable ranges
 shown in FIGS. 15A and 15B. In this case, output difference PE(n-2)
 satisfying the foregoing allowable range or larger than the reference
 value exists between the value of the throttle sensor at time T(n-3) and
 that of the throttle sensor at time T(n-2). Moreover, no output difference
 exists between the value of the throttle sensor at time T(n-2) and that of
 the throttle sensor at time T(n-1). In addition, also no output difference
 exists between the value of the throttle sensor at time T(n-1) and that of
 the throttle sensor at time T(n).
 In the foregoing case, the predicted correction terms 116 and 117 shown in
 FIG. 14 calculate predicted correction terms at time T(n-1) and time T(n).
 Thus, the throttle valve is operated on the assumption that the predicted
 opening of the throttle valve as indicated with an alternate long and
 short dash line has been obtained from the throttle sensor. The predicted
 opening of the throttle valve is the same as the output difference PE(n-2)
 between the value of the throttle sensor at time T(n-3) and that of the
 throttle sensor at time T(n-2).
 That is, the deviation PE(n-2) between the opening of the throttle valve at
 the previous time T(n-3) and the present opening of the throttle valve is
 calculated at time T(n-2). The deviation PE(n-2) is stored as a predicted
 value of the opening of the throttle valve at the next time T(n-1). If a
 fact is detected at time T(n-1) that no deviation exists between the
 present and pervious openings of the throttle valve, the detected opening
 of the throttle valve at time T(n-1) is made to be a value obtained by
 adding the deviation PE(n-2) calculated at the previous time T(n-2) to the
 opening of the throttle valve at time T(n-2).
 FIG. 17 is a time chart showing transition of the commanded value
 .theta.CM, that of opening of the throttle valve of each of the present
 invention and the conventional structure, that of the value of the
 throttle sensor and that of the integrated value (examples 1 and 2)
 realized when a commanded value .theta.CM of an opening .alpha., for
 example, 10.degree. has been output at time To. It is assumed that the
 opening of the throttle valve before time To is 0.degree. (in a completely
 closed state). In the foregoing case, the opening of the throttle valve
 passes the opener opening .theta.op to reach the commanded opening .alpha.
 after the commanded value .theta.CM of the opening .alpha. has been
 output.
 As can be understood from FIG. 17, when the opening of the throttle valve
 has been enlarged in accordance with the commanded value .theta.CM
 followed by the opening of the throttle valve reaches the opener opening
 .theta.op at time T(n-1), the conventional structure encounters a stoppage
 period for the throttle valve until time passes time T(n+4). The reason
 for this lies in that the integrated value is similar to that in the other
 periods in a period in which the value of the throttle sensor is not
 changed in a period from time T(n-1) to time T(n+3) in spite of change in
 the spring constant which acts on the rotational shaft of the throttle
 valve at the opener opening .theta.op.
 Therefore, when a fact that the value of the throttle sensor has not been
 changed from the value of the throttle sensor at time T(n-1) is detected
 at time T(n), the value of the throttle sensor at time T(n) is made as
 follows. That is, as indicated with an alternate long and short dash line,
 the value of the throttle sensor is the predicted value obtained by adding
 the deviation PE(n-1) of the value of the throttle sensor at time T(n-1)
 to the previous value of the throttle sensor. When a fact that the value
 of the throttle sensor has not been changed from the value of the throttle
 sensor at time T(n) is detected at time T(n+1), the value of the throttle
 sensor at time T(n+1) is made as follows. That is, as indicated with an
 alternate long and short dash line, the value of the throttle sensor is a
 predicted value obtained by adding the deviation PE(n-1) of the value of
 the throttle sensor at time T(n-1) to the previous value of the throttle
 sensor. That is, the value of the throttle sensor is the value obtained by
 adding a value which is two times the deviation PE(n-1) of the value of
 the throttle sensor at time T(n-1) to the value of the throttle sensor at
 time T(n+1). When a fact that the value of the throttle sensor has not
 been changed from the value of the throttle sensor at time T(n+1) is
 detected at time T(n+2), the value of the throttle sensor at time T(n+2)
 is made as follows. That is, as indicated with an alternate long and short
 dash line, the value of the throttle sensor is a predicted value obtained
 by adding the deviation PE(n-1) of the value of the throttle sensor at
 time T(n-1) to the previous value of the throttle sensor. That is, the
 value of the throttle sensor is the value obtained by adding a value which
 is three times the deviation PE(n-1) of the value of the throttle sensor
 at time T( n-1) t o the value of the throttle sensor at time T(n+2).
 Predicted correction term Ya at time T(n) is calculated by the following
 Equation (1) in accordance with the predicted value of the throttle sensor
 at time T(n):
EQU Ya=(PE(n-1.times.N).times.gain A (1)
 where N is the number of times at which a fact that the deviation between
 the previous value and the previous value detected by the throttle sensor
 is not a normal value and therefore, N=1 at time T(n). The gain A of the
 predicted correction term Ya is detected as a point on a plane PA of a
 two-dimensional map as shown in FIG. 18 in accordance with the position of
 the throttle sensor and the movement velocity of the throttle valve.
 Similarly, the predicted correction term Ya at time T(n+1) can be obtained
 by making N in the equation (1) to be 2in accordance with the predicted
 value of the throttle sensor at time T(n). The predicted correction term
 Ya at time. T(n+2) can be calculated by making N in the equation (1) to be
 3 in accordance with the predicted value of the throttle sensor at time
 T(n).
 At time T(n+3), the deviation between the value detected by the throttle
 sensor at time T(n+3) and the value detected by the throttle sensor at
 time T(n+2) is made to be larger than the foregoing reference value.
 Therefore, the value of the predicted correction term Ya is not
 calculated.
 After the predicted correction term Ya has been calculated, the value of
 the proportional calculation and the value of the integrating calculation
 are corrected. Only the value of the integrating calculation will now be
 described. The value of the integrating calculation is calculated as the
 following equation (2) by using the predicted correction term Ya:
EQU Value of Integrating Calculation=(Deviation .epsilon..times.Gain in
 Integration)+Ya (2)
 where deviation .epsilon. is the value in the rear of the adder Al shown in
 FIG. 14. The value of the integrating operation corrected with equation
 (2) is positioned between time T(n) and time T(n+3) shown in FIG. 17 as
 indicated with a solid line. When the deviation between the value detected
 by the throttle sensor at time T(n+3) and that detected by the throttle
 sensor at time T(n+2) is made to be larger than the foregoing reference
 value, the value of the predicted correction term Ya is not calculated at
 time T(n+3). The value of the integrating operation is restored to the
 original state. At this time, either of methods may be employed which
 include the method with which the value of the integration is immediately
 restored to the original state as shown in example 1 of FIG. 17 and the
 method with which the value of the integration is gradually restored to
 the original state as shown in example 2.
 Although the integrated value is corrected on the basis of a value of the
 predicted correction term Ya, also the differentiated value may similarly
 be corrected.
 The PID control according to this embodiment is structured such that when
 the value detected by the throttle sensor is free from change that is
 larger than the reference value, the predicted correction term Ya is
 calculated to correct the value of the proportion and the value of the
 integration. Thus, this embodiment is able to change the operation
 characteristic of the throttle valve 3 at the opener opening .theta.op.
 Therefore, the period of stoppage of the throttle valve 3 at the opener
 opening .theta.op can be shortened as indicated with a solid line H shown
 in FIG. 17. On the other hand, the conventional and simple PID control
 undesirably encounters elongation of the period of stoppage of the opening
 of the throttle valve near the opener opening .theta.op as indicated with
 a dashed line shown in FIG. 17. Therefore, the throttle valve 3 cannot
 smoothly be operated.
 In the foregoing embodiment, the next predicted opening of the throttle
 valve is previously calculated in accordance with the previous opening of
 the throttle valve and the present opening of the throttle valve. When the
 deviation between the previous opening of the throttle valve and the
 present opening of the throttle valve is smaller than the reference value
 K, the predicted opening of the throttle valve calculated previously is
 employed as the present opening of the throttle valve to correct the
 rotating force of the motor. As an alternative to this, a comparison may
 be made between the predicted opening of the throttle valve calculated
 previously and the present opening of the throttle valve. If the
 comparison results in a fact that the deviation is larger than reference
 value M, the rotating force of the motor may be corrected in accordance
 with the deviation.
 In the previous embodiment, the next predicted opening of the throttle
 valve is obtained in accordance with the deviation between the present
 opening of the throttle valve and the previous opening of the throttle
 valve. The next predicted opening of the throttle valve may be calculated
 by averaging the transition of the opening of the throttle valve which has
 occurred plural times.
 The example shown in FIG. 17 is arranged to perform control when the engine
 is accelerated by the opening of the throttle valve is enlarged. The
 control which is performed when the engine is decelerated by reducing the
 opening of the throttle valve may be structured such that the control for
 the acceleration process is inverted vertically. Therefore, the
 description of the foregoing control is omitted.
 An example of the control which is performed as described above by the
 control unit will now be described with reference to a flow chart shown in
 FIG. 19. The procedure shown in the foregoing flow chart is performed at
 each predetermined time Ts which is shorter than the sampling cycle T. The
 foregoing procedure controls the value of the integration as shown in
 example 1 of FIG. 17.
 In step 701, it is determined whether or not the present time is the
 sampling period T. If the present time is the sampling period T, the
 operation proceeds to step 702 where a present opening (the amount of
 depression of the acceleration pedal) detected by the accelerator opening
 sensor 15 is read as shown in FIGS. 3A and 3B. The read opening is made to
 be a present commanded value .theta.CM of the opening of the throttle
 valve. In step 703, opening/closing velocity V1 of the throttle valve is
 calculated in accordance with the magnitude of the commanded value
 .theta.CM. Then, the operation proceeds to step 704.
 The first opening/closing velocity V1 indicates a reference value for the
 following velocity of the opening of the throttle valve with respect to
 the commanded value .theta.CM. The opening/closing velocity V1 is required
 to be formed into a map so as to be stored in the ROM 103 so as to be
 determined in accordance with the magnitude of the commanded value
 .theta.CM at the time at which the opening/closing velocity V1 is
 calculated. Also the opening/closing velocity V1 of the throttle valve can
 be obtained by the present control. That is, also the opening/closing
 velocity V1 of the throttle valve can be obtained by producing a state
 equation by using parameters including the commanded value .theta.CM, the
 amount of depression of the accelerator pedal, the voltage of a batter and
 the temperature detected at the time at which the first opening/closing
 velocity V1 is calculated. Then the foregoing state equation is solved so
 that the opening/closing velocity VI is obtained.
 If it is determined in step 701 that the present time t1 is not the
 sampling period T, steps 702 and 703 are not performed. In this case, the
 operation proceeds to step 704.
 In step 704, the previous opening of the throttle valve .theta.tho is read.
 In step 705, the present opening of the throttle valve .theta.th is read
 as the present value. In step 706, the deviation .DELTA..theta.th between
 the previous and present openings of the throttle valve is calculated.
 Moreover, the movement velocity Vth of the throttle valve is calculated.
 In step 707, it is determined whether or not the absolute value of the
 deviation .DELTA..theta.th between the previous and present openings of
 the throttle valve calculated in step 706 is larger than the reference
 value K. If .vertline..DELTA..theta.th.vertline.&gt;K in step 707, the
 operation proceeds to step 708 where it is determined whether or not the
 movement velocity Vth of the throttle valve calculated in step 706 is
 larger than predetermined velocity L. If .vertline.Vth.vertline.&gt;L in step
 708, it is determined that the throttle valve has been smoothly followed
 the opening/closing velocity V1. Then, the operation proceeds to step 709.
 In step 709, on opening obtained by adding the deviation .DELTA..theta.th
 between the previous and present openings of the throttle valve calculated
 in step 706 to the present opening .theta.the of the throttle valve read
 in step 706 is made to be the next predicted opening .theta.th of the
 throttle valve. Moreover, the present predicted opening .theta.th of the
 throttle valve read in step 705 is stored as the previous opening
 .theta.tho of the throttle valve. Then, the number N of times at which the
 fact has been detected that the deviation between the previous and present
 values detected by the throttle sensor has exceeded the allowable range or
 the same is smaller than the reference value K is made to be zero. Then,
 the operation proceeds to step 710. In step 710, the drive duty ratio of
 the throttle motor is calculated for the usual PID control so as to be
 output. Thus, the foregoing routine is completed.
 If it is determined in step 707 that
 .vertline..DELTA..theta.th.vertline.&gt;K, or if it is determined in step 708
 that .vertline.Vth.vertline.&gt;L, the operation proceeds to step 711. In
 step 711, one is added to the number N of times at which the fact has been
 detected that the deviation between the previous detected value and the
 present detected value obtained by the throttle sensor has been made to be
 larger than the allowable range or a fact has been detected that the
 deviation has been smaller that the reference value K. Then, the operation
 proceeds to step 712. In step 712, the predicted opening .theta.the of the
 throttle valve calculated in the previous routine is read. In step 713,
 the number N calculated in step 711 and the predicted opening .theta.the
 of the throttle valve read in step 712 are used to calculate the predicted
 correction term Ya for the PID control in accordance with the foregoing
 equation (1). Instep 714, the predicted correction term Ya is subjected to
 the PID control in which the foregoing equation (2) is considered so that
 the drive duty ratio for the throttle motor is calculated and output.
 Thus, the foregoing routine is completed.
 The foregoing control is structured such that the next predicted opening of
 the throttle valve is previously calculated in accordance with the
 previous opening of the throttle valve and the present opening of the
 throttle valve. If the deviation between the previous opening of the
 throttle valve and the present opening of the throttle valve is not larger
 than the reference value K, the predicted opening of the throttle valve
 calculated previously is employed as the present opening of the throttle
 valve to correct the rotating force of the motor. Then, the procedure will
 now be described with reference to FIG. 20. The procedure is structured
 such that the predicted opening of the throttle valve calculated
 previously and the present opening of the throttle valve are compared with
 each other. If the comparison results in that the deviation between the
 two values is not smaller than the reference value M, the rotating force
 of the motor is corrected in accordance with the deviation.
 Steps 801 to 803 are the same as steps 701 to 703 shown in FIG. 19. Only
 when the present time is the sampling cycle T, the present amount of
 depression of the acceleration pedal is read to make the amount as the
 commanded value .theta.CM of the present opening of the throttle valve. In
 accordance with the magnitude of the commanded value .theta.CM, the
 opening/closing velocity V1 of the throttle valve is calculated. Then, the
 operation proceeds to step 804.
 In step 804, the pervious opening .theta.tho of the throttle valve and the
 predicted opening .theta.th of the throttle valve calculated previously
 are read. In step 805, the present opening .theta.th of the throttle valve
 is read as the present value. In step 806, the deviation .DELTA..theta.th
 between the previous and present openings of the throttle valve is
 calculated. Moreover, the movement velocity Vth of the throttle valve is
 calculated.
 In step 807, it is determined whether or not the absolute value
 .vertline..theta.th-.theta.the.vertline. of the deviation between the
 present opening .theta.th of the throttle valve read in step 805 and
 predicted opening .theta.the read in step 804 and calculated previously is
 smaller than the reference value M. If
 .vertline..theta.th-.theta.the.vertline.&lt;M in step 807, the operation
 proceeds to step 808 where it is determined whether or not the movement
 speed Vth of the throttle valve calculated in step 806 is larger than the
 predetermined velocity L. If .vertline.Vth.vertline.&gt;L in step 808, it is
 determined that the throttle valve smoothly follows the opening/closing
 velocity V1 of the throttle valve. Thus, the operation proceeds to step
 809. Steps 809 and 810 are the same as steps 709 and 710. In step 809, an
 opening obtained by adding the deviation .DELTA..theta.th between the
 previous and present openings of the throttle valve to the present opening
 .theta.th of the throttle valve is made to be a next predicted opening
 .theta.the of the throttle valve. Moreover, the present opening .theta.th
 of the throttle valve is stored as the previous opening .theta.tho of the
 throttle valve. The number N of the abnormal conditions is made to be
 zero. Then, a usual PID control is performed in step 810 so that the drive
 duty ratio for the throttle motor is calculated and output. Thus, the
 foregoing routine is completed.
 If it is determined in step 807 that
 .vertline..theta.th-.theta.the.vertline.&gt;M, or if it is determined in step
 808 that .vertline.Vth.vertline.&gt;L, the operation proceeds to step 811. In
 step 811, one is added to the number N of times at which the fact has been
 detected that the deviation between the present value detected by the
 throttle sensor and the present predicted opening of the throttle valve
 has been not smaller than the reference value M. Then, the operation
 proceeds to step 812. In step 812, the value of the number N of times
 calculated in step 811 and the predicted opening .theta.th of the throttle
 valve read in step 804 are used so that the predicted correction term Ya
 for the PID control is calculated in accordance with the following
 equation (3) which is similar to the foregoing equation (1):
EQU Ya=((.theta.the-.theta.tho).times.N).times.gain A (3)
 In step 813, the PID control is performed such that the predicted
 correction term Ya is considered with the equation (2) so that the drive
 duty ratio of the throttle motor is calculated and output. Thus, the
 foregoing routine is completed.
 FIG. 21 is a block diagram showing functions of the ECU 10 shown in FIG. 2
 to realize a fourth embodiment. The following arrangements are the same as
 those shown in FIG. 14. The structure of the PID control function 111 of
 the ECU 10 incorporates the differential operation function 111D, the
 proportional operation function 111P and integration operation function
 111I, the structure of the duty output calculating function 112, and the
 structure that the opening of the throttle valve which is operated by the
 throttle motor 4 is detected by the throttle opening sensor 5 so as to be
 fed back to the PID control function 111. Therefore, illustration of the
 same portions will be omitted.
 In the fourth embodiment, the foregoing usual control system for the
 throttle valve is further including a function 121 for storing opening
 .theta.th of the throttle valve, a function 122 for calculating deviation
 .DELTA..theta.th between the previous and present openings of the throttle
 valve, a function 123 for calculating predicted opening .theta.the of the
 throttle valve and a switch 124. The function 121 for storing opening
 .theta.th of the throttle valve stores the opening .theta.th of the
 throttle valve detected by the throttle opening sensor 5 at each cycle Ts,
 the opening .theta.th being stored together with detection time. The
 function 122 for calculating deviation .DELTA..theta.th between the
 previous and present openings of the throttle valve calculates the
 deviation .DELTA..theta.th between the previous opening .theta.tho stored
 in the function 121 for storing opening .theta.th of the throttle valve
 and the present opening .theta.th of the throttle valve so as to compare
 the deviation .DELTA..theta.th with the reference value M (refer to the
 first embodiment). In accordance with the deviation .DELTA..theta.th
 between the previous and present openings of the throttle valve calculated
 by the function 122 for calculating deviation .DELTA..theta.th between the
 previous and present openings of the throttle valve or in accordance with
 the past transition of the opening of the throttle valve stored in the
 function 121 for storing opening .theta.th of the throttle valve, the
 function 123 for calculating predicted opening .theta.the of the throttle
 valve predicts the opening .theta.the after a lapse of the cycle Ts. The
 predicted opening .theta.the of the throttle valve is stored.
 The function 122 for calculating deviation .DELTA..theta.th between the
 previous and present openings of the throttle valve connects the switch
 124 to the throttle opening sensor 5 when the deviation .DELTA..theta.th
 between the previous and present openings of the throttle valve is larger
 than the reference value M. When the deviation .DELTA..theta.th between
 the previous and present openings of the throttle valve is smaller than
 the reference value M, the switch 124 is connected to the function 123 for
 calculating predicted opening .theta.the of the throttle valve.
 If the deviation .DELTA..theta.th between the previous and present openings
 of the throttle valve is not smaller than the reference value M, a value
 detected by the throttle opening sensor 5 is fed back to the PID control
 function 111. When the deviation .DELTA..theta.th between the previous and
 present openings of the throttle valve is not larger than the reference
 value M, the previous predicted opening .theta.the of the throttle valve
 stored in the function 123 for calculating predicted opening .theta.the of
 the throttle valve is added to the PID control function 111. The foregoing
 operation will now be described with reference to FIG. 17. In a period
 from time T(n) to time T(n+2), the value of the throttle sensor indicated
 with an alternate long and short dash line is added to the PID control
 function 111. Therefore, the throttle valve can smoothly be operated.
 FIG. 22 is a block diagram showing functions of the ECU 10 shown in FIG. 2
 to realize a fifth embodiment. The following arrangements are the same as
 those shown in FIG. 14. The structure of the PID control function 111 of
 the ECU 10 incorporates the differential operation function 111D, the
 proportional operation function 111P and integration operation function
 111I, the structure of the duty output calculating function 112, and the
 structure that the opening of the throttle valve which is operated by the
 throttle motor 4 is detected by the throttle opening sensor 5 so as to be
 fed back to the PID control function 111. Therefore, the same portions are
 omitted from illustration.
 In the fifth embodiment, the foregoing usual control system for the
 throttle valve further includes a gain-constant changing switch 118, a
 gain-constant changing function 119 and a function 120 for calculating the
 deviation of the opening of the throttle valve. The gain-constant changing
 function 119 calculates the opening/closing velocity of the throttle valve
 when the gain-constant changing switch 118 is switched on. To change the
 amount of offset for changing the rotating force of the throttle motor in
 accordance with the opening/closing velocity, the gain-constant changing
 function 119 changes the gains of the differential operation function
 111D, the proportional operation function 111P and the integration
 operation function 111I.
 The gain-constant changing switch 118 is switched on/off in accordance with
 the output of the function 120 for calculating the deviation of the
 opening of the throttle valve. As described above, the function 120 for
 calculating the deviation of the opening of the throttle valve calculates
 the deviation .DELTA..theta.th between the present opening .theta.th of
 the throttle valve and the previous opening .theta.tho of the throttle
 valve by the cycle Ts to monitor the value of the deviation. When the
 deviation .DELTA..theta.th is larger than the reference value K, the
 function 120 for calculating the deviation of the opening of the throttle
 valve determines that the opening of the throttle valve is smoothly
 changed so that the state of the gain-constant changing switch 118 which
 is switched off is maintained. Then, the deviation .DELTA..theta.th is
 stored as the predicted opening .theta.the of a next opening of the
 throttle valve.
 If the deviation .DELTA..theta.th is not larger than the reference value K,
 the function 120 for calculating the deviation of the opening of the
 throttle valve determines that the opening of the throttle valve is not
 smoothly moved. Thus, the function 120 for calculating the deviation of
 the opening of the throttle valve switches the gain-constant changing
 switch 118 on. To make the level of the control signal output from the PID
 control function 111 to the duty output calculating function 112 to be the
 output level of the control signal realized when the previous predicted
 opening .theta.the of the throttle valve has been supplied to the PID
 control function 111, the gains of the differential operation function
 111D, the proportional operation function 111P and the integration
 operation function 111I are changed.
 Also the gain-constant changing switch 118 is not a mechanical switch and
 the switch is a flag for operating the gain-constant changing function
 119.
 As described above, the PID control according to the fifth embodiment, when
 the deviation .DELTA..theta.th between the previous and present openings
 of the throttle valve is not larger than the reference value K, the
 operation characteristic of the throttle valve 3 can be changed.
 Therefore, the opening of the throttle valve 3 can smoothly be changed.
 Therefore, if the opening of the throttle valve passes the opener opening
 .theta.op, the force for operating the throttle valve can greatly be
 changed. As a result, the throttle valve can smoothly be operated in the
 vicinity of the opener opening.