JPH06213021A - Valve timing control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent under shoot of engine rotation and occurrence of engine stall in the case where a throttle is closed rapidly at the time of low car speed or of such a condition as no-load at low car speed. CONSTITUTION:A variable valve timing mechanism 23 consists of a timing pulley 24 and a step motor 25, and the opening/closing timing of an intake valve 9 is varied continuously. In a VVTECU 41, a restricted target step number for controlling the opening/closing timing of an intake valve 9 in the case when car speed is a prescribed speed or less is set as VLim on the basis of car speed SP. In the VVTECU 41, the restricted target step number VLim is compared with a target step number after correcting a water temperature. Even if the target step number after correcting the water temperature is larger than the restricted target step number VLim, the restricted target step number VLim is set as a target step number for controlling the opening/closing timing of the intake valve 9. In the VVTECU 41, the variable valve timing mechanism 23 is controlled on the basis of the target step number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve timing control device equipped with a variable valve timing mechanism for continuously changing the opening / closing timing of an intake valve or an exhaust valve according to the operating state of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, when the output control of an internal combustion engine is controlled by the vehicle or the operating state of the internal combustion engine, as disclosed in Japanese Patent Laid-Open No. 61-65036, the vehicle speed is considered in consideration of stability during idling. When is zero, or under an idle condition, the overlap period is controlled to be short.

[0003]

However, when the vehicle speed is low or the throttle is suddenly closed under no load condition, the variable valve timing mechanism is controlled from the advance angle to the retard angle, but the variable valve timing mechanism operates. Due to the delay, there is a state in which the overlap period is long at a low intake air amount. Therefore, when the vehicle speed is low or when the throttle is rapidly closed under no load, there is a problem that misfire, combustion failure, etc. occur and undershoot of engine rotation or engine stall occurs.

An object of the present invention is to continuously control the valve timing on the basis of the engine speed of the internal combustion engine and the intake air amount, and to open the throttle at a low vehicle speed such as a low vehicle speed or no load condition. An object of the present invention is to provide a valve timing control device for an internal combustion engine that can prevent an engine rotation undershoot and an engine stall when the engine is suddenly closed.

[0005]

In order to solve the above problems, the present invention, as shown in FIG. 1, is driven at a predetermined timing in synchronism with the rotation of an internal combustion engine M1 mounted on a vehicle to perform combustion. Intake passage M3 and exhaust passage M4 leading to the chamber M2
Intake valve M5 and exhaust valve M6 to open and close
A variable valve timing mechanism M7 driven to continuously change the opening / closing timing of at least one of the intake valve M5 and the exhaust valve M6; and an operating state detecting means for detecting the operating state of the internal combustion engine M1. M8
And a drive control means M9 for driving and controlling the variable valve timing mechanism M7 to control the opening / closing timing based on the detection result of the operating state detection means M8. The vehicle speed detection means M10 for detecting the vehicle speed and the setting means M11 for setting the valve timing limit advance value on the basis of the vehicle speed data from the vehicle speed detection means M10. In the following cases, the gist is to control the opening / closing timing of the variable valve timing mechanism M7 in the drive control means M9 based on the valve timing limit advance value set by the setting means M10.

[0006]

With the above structure, as shown in FIG. 1, the intake valve M5 and the exhaust valve M6 are operated when the internal combustion engine M1 is in operation.
Is driven at a predetermined timing in synchronism with the rotation of the internal combustion engine M1, and the intake passage M3 and the exhaust passage M4 are opened and closed to intake and exhaust the combustion chamber M2. or,
The operating state detecting means M8 detects the operating state of the internal combustion engine,
The drive control means M9 drives and controls the variable valve timing mechanism M7 to control the opening / closing timing of the internal combustion engine M1 based on the detection result of the operating state detection means M8.

Further, the setting means M11 is a vehicle speed detecting means M.
A valve timing limit advance value is set based on the vehicle speed data from 10. Then, the drive control means M9 is based on the valve timing limit advance value set by the setting means M10 when the vehicle speed is equal to or lower than the predetermined speed.
Control the opening / closing timing of the variable valve timing mechanism M7.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying a valve timing device for an internal combustion engine according to the present invention will be described below with reference to FIGS.

FIG. 2 is a schematic configuration diagram (only one cylinder is shown) for explaining a gasoline engine 1 as an internal combustion engine mounted on the vehicle of this embodiment. A piston 3 is vertically movable in a cylinder bore 2a formed in a cylinder block 2 of the engine 1. The piston 3 is connected to a crankshaft (not shown) via a rod 4. A space surrounded by the piston 3, the cylinder bore 2a, and the cylinder head 5 covering the bore 2a is a combustion chamber 6.

An intake passage 7 and an exhaust passage 8 are provided in the combustion chamber 6 so as to communicate with each other. An intake valve 9 for opening and closing is attached to an intake port 7a that opens into the combustion chamber 6 of the intake passage 7. Further, an exhaust valve 10 for opening and closing is attached to the exhaust port 8a opening to the combustion chamber 6 of the exhaust passage 8.

Outside air is introduced into the intake passage 7 through an air cleaner (not shown). In addition, the injector 1 for fuel injection is provided in the intake passage 7 in the vicinity of the intake port 7a.
1 is provided so that fuel is taken into the intake passage 7. As is well known, the injector 11 is supplied with fuel of a predetermined pressure from a fuel tank (not shown) by the operation of a fuel pump.
Then, the mixture of the fuel and the outside air injected from the injector 11 and taken into the intake passage 7 becomes the intake valve 9
When it is opened, it is introduced into the combustion chamber 6 through the intake port 7a. In addition, when the air-fuel mixture introduced into the combustion chamber 6 is exploded and burned, the driving force of the engine 1 is obtained via the piston 3 and the crankshaft. Further, the burned gas combusted in the combustion chamber 6 is discharged to the outside from the exhaust port 8a through the exhaust passage 8 when the exhaust valve 10 is opened.

In the middle of the intake passage 7, the accelerator pedal 1
A throttle valve 13 that is opened / closed in association with the operation of 2 is provided. Then, by opening / closing the throttle valve 13, the amount of intake air to the intake passage 7 is adjusted.

In the vicinity of the throttle valve 13, a throttle sensor 14 as a throttle detecting means for detecting the throttle opening TA, and when the throttle valve 13 is at the fully closed position, the switch is turned on and a fully closed signal LL is output. Full-closed switches 14a for outputting are respectively provided.
A surge tank 15 that smoothes the pulsation of the intake air amount is provided downstream of the throttle valve 13. Further, a well-known air flow meter 16 that detects the amount of intake air taken into the intake passage 7 from the outside is provided on the upstream side of the throttle valve 13.

Next, a valve mechanism for the intake valve 9 and the exhaust valve 10 will be described. The intake valve 9 and the exhaust valve 10 are stems 9a and 10 extending upward, respectively.
a, and valve springs 17, 18 and valve lifters 19, 20 and the like are respectively attached to the upper portions of the stems 9a, 10a. Cams 21a and 22a are provided on the valve lifters 19 and 20 so as to engage with them. The cams 21a and 22a are formed on the intake-side camshaft 21 and the exhaust-side camshaft 22 supported by the cylinder 5, respectively, for all cylinders. Then, the intake valve 9 and the exhaust valve 10 are moved upward by the urging force of the valve springs 17 and 18,
Moreover, the intake port 7a and the exhaust port 8a are urged in the direction of closing. In this biased state, each stem 9a, 1
The upper end of 0a is always in contact with the cams 21a and 22a via the valve lifters 19 and 20.

In this embodiment, the intake side camshaft 21 is made variable so that only the opening / closing timing of the intake valve 9 is variable.
The variable valve timing mechanism (hereinafter simply referred to as "V
A timing pulley assembly 24 and a step motor 25, which constitute a “VT” 23, are provided. The step motor 25 includes a plurality of electromagnetic coils, and by sequentially selecting the electromagnetic coils to be excited, the step motor 25 rotates in a predetermined direction for each step. On the other hand, only the timing pulley 26 is provided at the tip of the camshaft 22 on the exhaust side. The timing pulley assembly 24 and the timing pulley 26 are drivingly connected to the crankshaft via a timing belt (not shown).

Therefore, when the engine 1 is in operation, power is transmitted from the crankshaft to the timing pulley assembly 24 and the timing pulley 26 via the timing belt, so that the camshafts 21 and 22 are rotationally driven to drive the cams. 21a and 22a are rotated respectively. Further, the valve lifters 19 and 20 are pressed against the biasing forces of the valve springs 17 and 18 in accordance with the profiles of the rotated cams 21a and 22a,
The intake valve 9 and the exhaust valve 10 move downward, and the intake port 7a and the exhaust port 8 are opened. As is well known, the basic opening and closing timings of the intake valve 9 and the exhaust valve 10 are four strokes of the piston 3 (intake stroke, compression stroke,
It is set in advance relative to the vertical movement associated with the expansion stroke and the exhaust stroke. Here, the air-fuel mixture is sucked into the combustion chamber 6 when the intake port 7a is opened by the downward movement of the piston 3 during the intake stroke, that is, when the intake valve 9 is opened. Further, when the exhaust port 8a is opened by the upward movement of the piston 3 during the exhaust stroke, that is, when the intake valve 10 is opened, the burned gas is discharged from the combustion chamber 6 to the exhaust passage 8.

The VVT 23 on the intake side is drive-controlled to change the basic opening / closing timing of the intake valve 9 according to the operating state at that time, and the camshaft 2
1, the rotation phase of each cam 21a is appropriately changed. That is, the VVT 23 on the intake side is drive-controlled to change the intake timing of the air-fuel mixture into the combustion chamber 6. By changing the basic opening / closing timing of the intake valve 9, the valve overlap between the intake valve 9 and the exhaust valve 10 is changed.

In order to ignite the air-fuel mixture introduced into the combustion chamber 6, the spark plug 2 is attached to the cylinder head 5 at the center of the cylinder.
7 is fixed, and its discharge portion 27a is arranged in the combustion chamber 6. This spark plug 27 is the distributor 2
It is driven based on the ignition signal distributed at 8. The distributor 28 is for distributing the high voltage output from the igniter to the spark plug 27 in synchronization with the crank angle of the engine 1. The distributor 28 includes a rotor 28a that is rotated in association with the rotation of the engine 1.
Is provided, and a rotation speed sensor 30 that detects the engine rotation speed NE from the rotation of the rotor 28a is provided.
Further, the distributor 28 detects the crank angle reference position of the engine 1 at a predetermined ratio according to the rotation of the rotor 28a, and outputs the reference signal G to the cylinder determination sensor 3
1 is provided.

The throttle sensor 14, the fully closed switch 14a, the air flow meter 16, and the rotation speed sensor 3 described above.
0, the starter switch 39, and the cylinder discrimination sensor 31 constitute an operating state detecting means for detecting the operating state of the engine 1. In addition to this, the temperature of the cooling water of the engine 1 ( Cooling temperature) T
A water temperature sensor 32 that detects HW is attached. The water temperature sensor 32 also serves as a temperature detecting means for detecting the temperature of the engine 1. An oxygen sensor 33 that detects the oxygen concentration in the exhaust gas is attached in the middle of the exhaust passage 8. Further, in this embodiment, the vehicle speed sensor 3 as a vehicle speed detecting means for detecting the traveling speed (vehicle speed) SP of the vehicle.
4 are provided. The vehicle speed sensor 34 is attached to a transmission (not shown) and is driven by rotation of its gear. In addition, in this embodiment, there is provided a brake sensor 36 which detects the operation of the brake pedal 35 operated for vehicle braking, turns it "on", and outputs the brake signal BS.

A brake booster 37 is connected to the brake pedal 35. The brake booster 37 includes a one-way valve 37a, and the valve 37a communicates with the intake passage 7 downstream of the throttle valve 13 through a communication pipe 37b. As is well known, the brake booster 37 is a braking force multiplying device that uses the negative pressure of the intake passage 7, and a description of the structure thereof will be omitted here.

Further, in this embodiment, the engine 1 is provided with a starter 38 for applying a rotational force by cranking at the time of starting the engine 1. Also, this starter 3
8 is provided with a starter switch 39 for detecting its on / off operation. As is well known, starter 38
Is turned on and off by operating an ignition switch (not shown). While the ignition switch is being operated, the starter 38 is turned on and the starter switch 39 outputs the starter signal ST. ing.

As shown in FIG. 2, the throttle sensor 14, the fully closed switch 14a, the air flow meter 16, the rotation speed sensor 30, the cylinder discrimination sensor 31, the water temperature sensor 32, the oxygen sensor 33, the vehicle speed sensor 34, and the starter as described above. The switch 39 and the like are electrically connected to the input side of an engine electronic control unit (hereinafter simply referred to as “engine ECU”) 40. The injector 11 and the igniter 29 described above are electrically connected to the output side of the engine ECU 40. Then, the engine ECU 4
0 suitably controls the injector 11 and the igniter 29 based on the output signals from the fully closed switch 14a, the air flow meter 16, the sensors 14, 30 to 34, and the starter switch 39.

The engine ECU 40 is a control device that mainly controls the fuel amount control device and the ignition timing control of the engine 1. In addition to this, in this embodiment, as shown in FIG.
A VVTECU 41, which constitutes drive control means and setting means for controlling the drive of the VVT 23, is provided. The VVTECU 41 controls the rotation direction and the rotation amount of the output shaft of the step motor 25. Therefore, the engine ECU 4 is provided on the input side of the VVTECU 41.
From 0 to throttle opening TA, fully closed signal LL, engine speed NE, cooling water temperature THW, vehicle speed SP, starter signal S
The detected values of T and the intake air amount Ga, etc. are input as data signals. Further, the brake signal BS from the brake sensor 36 is input to the input side of the VVTECU 41.
Further, in order to control the opening / closing timing of the intake valve 9, the VVTECU 41 determines the magnitude of valve overlap according to the operating state of the engine 1 at that time based on the input data signal or the like, and the step motor 25 is preferably set. A valve timing control signal for controlling is output from the output side.

Next, the engine ECU 40 and VVTE
The configuration of the CU 41 will be described with reference to the block diagrams of FIGS. FIG. 3 is a block diagram illustrating the electrical configuration of the engine ECU 40. The engine ECU 40 includes a central processing unit (CPU) 42, a read-only memory (ROM) 43 in which a predetermined control program and the like are stored in advance, a CP
A theory in which a random access memory (RAM) 44 for temporarily storing the operation result of U42, a backup RAM 45 for storing prestored data, and the like, and each of these units, an external input circuit 46, an external output circuit 47, etc., are connected by a bus 48. It is configured as an arithmetic circuit.

The external input circuit 46 includes the throttle sensor 14, the fully closed switch 14a, and the air flow meter 1.
6, a rotation speed sensor 30, a cylinder discrimination sensor 31, a water temperature sensor 32, an oxygen sensor 33, a vehicle speed sensor 34, and a starter switch 39 are connected to each other. On the other hand, the injector 11, the igniter 29, and the VVTECU 41 are connected to the external output circuit 47, respectively.

Then, the CPU 42 reads the signals from the fully closed switch 14a, the air flow meter 16, the sensors 14, 30 to 34, the starter switch 39, etc., which are input via the external input circuit 46, as input values. When reading this input value, the external input circuit 46 uses the throttle sensor 14, the air flow meter 16, and the water temperature sensor 3.
2 and the input values from the oxygen sensor 3 are subjected to analog / digital conversion processing. Also, the external input circuit 4
6, the input values from the rotation speed sensor 30, the cylinder discrimination sensor 31, the vehicle speed sensor 34, etc. are subjected to waveform shaping processing. Then, the CPU 42 causes the fully closed switch 14
a, air flow meter 16, each sensor 14, 30-34
Also, the injector 11, the igniter 29, etc. are suitably controlled based on the input value read from the starter switch 39, etc.

The CPU 42 also selects the throttle opening T from the signals read from the fully closed switch 14a, the air flow meter 16, the sensors 14, 30 to 34, the starter switch 39, etc. as input values via the external input circuit 46.
A, fully closed signal LL, engine speed NE, cooling water temperature TH
W, the starter signal ST, the intake air amount Ga, and the like are output to the VVTECU 41 via the external output circuit 17 as data signals.

FIG. 4 is a block diagram for explaining the electrical construction of the VVTECU 41. VVT ECU 41 is a micro processing unit (MPU) 50, VVT 2
R in which a predetermined control program for 3 etc. is stored in advance
RA for temporarily storing the calculation results of the OM51 and MPU50
It is configured as a theoretical operation circuit in which the M52 and the like and each of these parts, the input / output port 53, the output port 54, and the like are connected by a bus 55. Further, the VVTECU 41 is a clock generator 5 that generates a periodic clock pulse.
6, a clock pulse is supplied from the generator 56 to the MPU 50. Furthermore, VV
The TECU 41 includes a latch circuit 57 and a gate 58 connected to the output port 54 thereof.

The input / output circuit 53 is connected to the engine ECU 40. A brake sensor 36 is connected to the input / output port 53, and the step motor 25 is connected to the gate 58.
Are connected.

Then, the MPU 50 inputs the throttle opening TA, which is input through the input / output port 53, the fully closed signal LL,
Engine speed NE, cooling water temperature THW, starter signal S
Signals such as T, the intake air amount Ga, and the brake signal BS are read as input values, and the step motor 25 is suitably controlled based on the read input values. That is, MPU5
0 determines the direction in which the step motor 25 should rotate and the number of steps according to the control program stored in the ROM 51 based on the read input value, and the result of the calculation is used as a valve timing control signal via the output port 54 and the latch circuit 57. Output to. The latch circuit 57 receives the valve timing control signal and outputs an opening / closing command of the gate signal 58 according to a predetermined sequence to execute the valve timing control signal. Then, the gate 58 follows the opening / closing command,
The electromagnetic coil to be excited is selected and the step motor 25 is driven.

Next, the structure of the VVT 23 will be described with reference to FIG. The intake-side cam shaft 21 that drives the intake valve 9 is rotatably supported by the cylinder head 5 by the cam journal 21b. And
At the tip of the cam shaft 21, a timing pulley assembly 24 and a step motor 25, which form a VVT 23, are provided. The timing pulley assembly 24 is composed of a pulley body 62 having a plurality of outer teeth 61 on the outer circumference, an inner cap 63 and a cylindrical gear 64 mounted on the pulley body 62.

That is, the pulley body 62 is provided with a boss 62a and a circumferential wall 62b near the center thereof.
A circumferential groove 62c is formed between a and the circumferential wall 62b.
Helical teeth 62d are formed on the inner circumference of the circumferential wall 62b. The pulley main body 62 is assembled on the cam shaft 21 by the boss 62a so as to be relatively rotatable.
On the other hand, the inner cap 63 includes a large tubular portion 63a and a small tubular portion 63b extending to the opposite side, and helical teeth 63c are formed on the outer circumference of the large tubular portion 63a. The large cap portion a of the inner cap 63 is fitted so as to cover the boss 62a, and is assembled so as to be rotatable relative to the pulley body 62. The inner cap 63 is integrally rotatably fixed to the tip of the camshaft 21 by a bolt 65 and a knock pin 66. Further, the cylindrical gear 64 has an outer peripheral wall 64.
a and the inner peripheral wall 64b, and the bottom wall has a hole 64
c is formed. Helical teeth 64d and 64e are formed on the inner and outer circumferences of the inner peripheral wall 64b, respectively.
A circumferential groove 64f is formed between the inner peripheral wall 64b and the inner peripheral wall 64b. Then, the inner peripheral wall 64b of the cylindrical gear 64 and the circumferential groove 64
f is the circumferential wall 62b and the circumferential groove 62c of the pulley body 62.
It has been assembled due to unevenness.

In this assembled state, each helical tooth 6
2d, 63c, 64d, and 64e are meshed with each other, and due to the meshing relationship, the cylindrical gear 64 can rotate relative to the camshaft 21 by moving in the axial direction. Further, the timing pulley assembly 24 is drivingly connected to the crankshaft via a timing belt (not shown) that is fitted around the outer teeth 61 of the pulley body 62.

Therefore, by drivingly transmitting from the crankshaft to the timing pulley assembly 24, the pulley body 62 and the inner cap 6 connected by the cylindrical gear 64.
3 and the cam shaft 21 connected to the inner cap 63 by the bolt 65 and the knock pin 66 are integrally rotated.

The step motor 25 is attached to the engine 1 by a bracket (not shown). The step motor 25 is for moving the cylindrical gear 64 in the axial direction, and a worm gear 67 having a cylindrical shape and having teeth 67a on the outer periphery is attached to the output shaft thereof.
The worm gear 67 is a small cylinder portion 63b of the inner cap 63.
It is fitted so as to be rotatable relative to the cylindrical gear 6
It is arranged so as to penetrate the four holes 64c. On the other hand, around the hole 64c of the cylindrical gear 64, a ring gear 68 having teeth 68a on the inner circumference is mounted by a ball bearing 69 so as to be relatively rotatable.

The ring gear 68 meshes with the outer circumference of the worm gear 67, and due to the meshing relationship, rotation of the worm gear 67 enables axial movement. In order to prevent the ring gear 68 from rotating, a long groove 68b extending in the axial direction is formed on the outer periphery of the ring gear 68 on the step motor 58 side. At the same time, a detent member 70 having a tubular shape and extending toward the timing pulley assembly 24 is attached to the casing of the step motor 25. The ring gear 68 is provided on the inner periphery of the rotation preventing member 70 due to the engagement between the protrusion 70a engaging with the long groove 68b and the long groove 68b.
Is prevented from rotating and only movement in the axial direction is allowed.

Therefore, when the timing pulley assembly 24 and the cam shaft 21 are integrally rotated, the step motor 25 is driven to rotate the worm gear 67 in a certain direction by a predetermined amount, whereby the ring gear 68 is rotated.
Is moved in the axial direction while being prevented from rotating on the worm gear 67. Along with this, the cylindrical gear 64 is moved in the same axial direction, and relative rotation occurs between the pulley main body 62 and the cam shaft 21, so that the cam shaft 21 is twisted.
As described above, in the VVT 23 of this embodiment, the step motor 25 is drive-controlled to change the axial position of the cylindrical gear 64, and as a result, the camshaft 21 is twisted. And camshaft 2
By imparting a twist to 1, the opening / closing timing of the intake valve 9 is changed and the valve overlap is changed.

The oil passage 7 is provided inside the camshaft 21.
1, 72 are formed, and the lubricating oil is supplied to the inside of the timing pulley assembly 24 through the oil passages 71, 72.

Now, the operation of the valve timing control system for an internal combustion engine constructed as described above will be described with reference to FIGS.
Follow the instructions below. 6 and 7 are flowcharts of a main routine and a VVT control routine executed by the VVT ECU 41 for controlling the drive of the VVT 23, which are executed every predetermined time.

First, in the main routine, step 101
The throttle sensor 14, the fully closed switch 14a, the rotation speed sensor 30, the water temperature sensor 32, and the starter switch 3
9. Throttle opening T detected by the vehicle speed sensor 34
A, fully closed signal LL, engine speed NE, cooling water temperature TH
W, the starter signal ST, the vehicle speed SP, and the intake air amount Ga are read from the engine ECU 40, respectively. Further, the brake signal BS detected by the brake sensor 36 is read.

In step 102, based on the water temperature THW previously read, a function f (T
After setting the calculation result of (HW) as the correction step number VTHW for controlling the opening / closing timing of the intake valve 9, the process proceeds to step 103. The calculation of the function f (THW) is performed with reference to the map shown in FIG. In step 103, based on the vehicle speed SP previously read, the function f (S
P) is calculated, and the calculation result is set as the limit target step number VLim for controlling the opening / closing timing of the intake valve 9. The limit target step number is the motor step number of the step motor 25 corresponding to the valve timing limit advance value, and 250 steps corresponds to the advance value of 50 ° in this embodiment. The calculation of the function f (SP) is performed with reference to the map shown in FIG. This map shows the vehicle speed S as shown in FIG.
If P is less than or equal to the predetermined speed, the target number of limit steps V
Lim is set to be proportional to the vehicle speed, and when exceeding a predetermined speed, the limit target step number VLim is set to a fixed value of 250 steps.

Next, the "VVT control routine" will be described with reference to FIGS. In step 104, it is determined whether or not the starter signal ST is "on", that is, whether or not the engine 1 is being started. If the starter signal ST is "on" here, it is assumed that the engine is starting, and in step 107 the target step number VSTBASE for controlling the step motor 25 corresponding to the target advance value (fixed value) after starting is targeted. Set as the number of steps Vst. In step 104, the starter signal ST is "on".
If not, it is assumed that the engine 1 has been started,
In step 105, it is determined whether the fully closed signal LL is "on", that is, whether it is during deceleration or idle. Here, when the fully closed signal LL is "on", it is determined that the vehicle is decelerating or idling, and the process proceeds to step 107.

If the fully closed signal LL is not "ON" in step 105, it is determined that the vehicle is running normally without deceleration or idling, and the process proceeds to step 106. Step 1
At 06, based on the engine speed NE and the intake air amount Ga previously read by the main routine, a function f (NE, Ga) having these values as parameters is calculated, and the calculation result is opened / closed of the intake valve 9. After setting the target step number Vst for timing control, step 108
Move to. The calculation of this function f (NE, Ga) is performed in advance by R
It is performed with reference to the map stored in the OM 51.

Then, in step 108, step 1
06 or the target step number Vst after water temperature correction is obtained by subtracting the correction step number VTHW from the target step number Vst set in step 107, and the process proceeds to step 109. In step 109, the limited target step number VLim obtained in the main routine is compared with the target step number after water temperature correction calculated in step 108. Then, the target step number Vst after the water temperature correction is the limit target step number V
If it is larger than Lim, the limit target step number VLim is set as the target step number Vst. If the target step number Vst after water temperature correction is less than or equal to the limit target step number VLim, the process proceeds to step 111.

That is, when the vehicle speed is equal to or lower than the predetermined speed, the limit target step number corresponding to the speed is set, and if the target step number after water temperature correction is larger than the limit target step number, the limit is added. This prevents the valve overlap period from increasing.

Next, at step 111, the result obtained by subtracting the current step number Vpo at the step motor 25 from the set target step number Vst is the control step number ST.
Set as EP. In step 112, it is determined whether the control step number STEP is "0". Here, when the control step number STEP is “0”,
The subsequent processing is temporarily terminated without driving the step motor 25. On the other hand, if the control step number STEP is not "0" in step 112, it is determined in step 113 whether the control step number STEP is larger than "0", that is, whether the control step number STEP is a positive number. To judge. If the control step number STEP is a positive number, the control flag DIR is reset to "0" in step 114, and then step 1
Go to 17.

When the control step number STEP is a negative number in step 113, step 115
The control flag DIR is set to "1". Next, in step 116, after setting the absolute value of the control step number STEP as a new control step number STEP,
Control goes to step 117. Then, in step 117, it is determined whether or not the control flag DIR is "1". If the control flag DIR is “1”, the step motor 25 of the intake side VVT 23 is determined in step 118.
Is reversed by one step and then the process proceeds to step 120. When the control flag DIR is "0", the step motor 25 is rotated forward by one step in step 119, and then the process proceeds to step 120.

At step 120, the control step number STE
The result of subtracting "1" from P is set as the new control step number STEP. Then, in step 121, the newly set control step number STEP is "0".
Or not. If the new control step number is not "0", the process jumps to step 117 and the processes of steps 117 to 121 are repeated.
That is, the intake side VVT 23 is drive-controlled.

On the other hand, when the new control step number STEP is "0" in step 121, the subsequent processing is temporarily terminated. In this way, the VVT 23 is drive-controlled by the control of the step motor 25, and the opening / closing timing of the intake valve 9 is controlled.

As described above, in this embodiment, when the vehicle speed is equal to or lower than the predetermined speed, the limit target step number corresponding to the speed is set, and if the target step number after water temperature correction is larger than the limit target step number. The number of target steps is limited. This prevents the valve overlap period from increasing when the vehicle speed is equal to or lower than the predetermined speed.

Therefore, when the vehicle speed is low, or when the throttle is suddenly closed at low vehicle speed with no load, the valve overlap period does not increase even if the intake air amount becomes small, so that misfire or combustion occurs. No defects will occur. Therefore, it is possible to prevent undershoot of engine rotation and engine stall. In particular,
In the case of an AT vehicle, a load is likely to be applied to the engine 1 due to the torque converter, but the control of the present embodiment is effective in preventing engine stall and engine rotation undershoot.

The present invention is not limited to the above-mentioned embodiment, and can be arbitrarily modified within a range not departing from the spirit of the present invention. (1) In the above-described embodiment, the VVT 23 that makes only the opening / closing timing of the intake valve 9 variable is provided.
It is also possible to provide a VVT that makes only the opening / closing timing of 0 variable, or a VVT that makes the opening / closing timing of both the intake valve 9 and the exhaust valve 10 variable.

(2) In the above embodiment, the step motor 2
Although the intake side VVT 23 having a drive limit of 5 is adopted, a hydraulically driven VVT can also be adopted. (3) In the above embodiment, the gasoline engine 1 is embodied, but it may be embodied as a diesel engine.

(4) In the above-described embodiment, steps 102 and 103 are performed in the main routine, but these steps may be performed in the interrupt routine every 1 second.

[0055]

As described in detail above, according to the present invention,
When continuously controlling the valve timing based on the engine speed of the internal combustion engine and the intake air amount, when the vehicle speed is low or the throttle is suddenly closed at low vehicle speed such as no load condition, the engine speed Undershoot of
The occurrence of engine stall can be prevented. or,
Since the combustion failure does not occur, it has an excellent effect of preventing the generation of emission.

[Brief description of drawings]

FIG. 1 is a conceptual configuration diagram illustrating a basic conceptual configuration of the present invention.

FIG. 2 is a schematic configuration diagram illustrating a gasoline engine in one embodiment embodying the present invention.

FIG. 3 is a block diagram showing an electrical configuration of the engine ECU of the same.

FIG. 4 is a block diagram showing an electrical configuration of VVT ECU.

FIG. 5 is a sectional view showing the structure of the VVT.

FIG. 6A is a flowchart explaining a “main routine” executed by the VVTECU, and FIG.
3 is a flowchart illustrating a "VVT control routine" that is also executed by VVT ECU.

FIG. 7 is a flowchart similarly illustrating a “VVT control routine”.

FIG. 8 is a map similarly defining a relationship of the correction step number corresponding to the correction advance value with respect to the water temperature THW in advance.

FIG. 9 is a map similarly defining a relationship between a vehicle speed and a target number of steps corresponding to a limit advance value.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine as an internal combustion engine, 6 ... Combustion chamber, 7 ... Intake passage, 8 ... Exhaust passage, 9 ... Intake valve, 10 ... Exhaust valve, 23 ... VVT, 14 ... Throttle sensor, 14a ...
Full-closed switch, 30 ... Revolution sensor, 34 ... Vehicle speed sensor as vehicle speed detecting means, 39 ... Starter switch (1
4, 30, 39 constitute an operating state detecting means),
41 ... VVTEC constituting setting means and drive control means
U.

Claims (1)

[Claims] 1. An intake valve and an exhaust valve, which are driven at a predetermined timing in synchronization with the rotation of an internal combustion engine mounted on a vehicle to open and close an intake passage and an exhaust passage communicating with a combustion chamber, respectively, and the intake valve and the exhaust valve. A variable valve timing mechanism that is driven to continuously change the opening / closing timing of at least one of the exhaust valves, an operating state detection unit that detects the operating state of the internal combustion engine, and a detection result of the operating state detection unit. A valve timing control device for an internal combustion engine, comprising: a drive control means for driving and controlling the variable valve timing mechanism to control the opening / closing timing based on a vehicle speed detection means for detecting a vehicle speed of the vehicle; Setting means for setting a valve timing limit advance value based on vehicle speed data from The control means controls the opening / closing timing of the variable valve timing mechanism in the drive control means based on the valve timing limit advance value set by the setting means when the vehicle speed is equal to or lower than a predetermined speed. Valve timing control device.