JPH0676767B2 - Engine torque control method when switching valve operating characteristics - Google Patents

Description

Detailed Description of the Invention a. Object of the Invention (Industrial field of use) The present invention relates to an engine control method in which the valve operating characteristics of intake and exhaust valves are variable.

The switching of the valve operating characteristics means switching at least one of the opening / closing timing of the intake valve or the exhaust valve, the opening period, and the valve lift amount, and at least one of a plurality of intake valves or exhaust valves in one cylinder. It also includes making the valve open period substantially zero and switching it to the closed state.

(Prior Art) An engine in which the valve operating characteristics of the intake valve and / or the exhaust valve can be switched between a low speed valve operating characteristic suitable for a low rotation range and a high speed valve operating characteristic suitable for a high rotation range. However, it is disclosed in Japanese Examined Patent Publication No. 49-33289, in which the low speed valve operating characteristic is set in the region where the engine speed is below a predetermined value and the intake negative pressure is below a predetermined value (vacuum side). Switching, and in other areas switches to high speed valve operating characteristics.

Further, in the valve operating characteristic switching control method proposed in Japanese Patent Application No. 63-192239, the output (torque) when using the low speed valve operating characteristic and the output (torque) when using the high speed valve operating characteristic are The valve operating characteristics are switched at the points where they substantially coincide.

(Problems to be Solved by the Invention) When the switching method as described above is used, a shock associated with a change in engine torque at the time of switching as described below becomes a problem.

First, it is due to hysteresis for stabilizing the switching operation. In general, in order to prevent frequent switching operations, the switching point of the valve operating characteristic from one to the other is set at the point where the torques in both valve operating characteristics match, and the opposite, that is, the switching from the other to one is performed. The points are set by providing hysteris and shifting them from the torque coincidence points. Then, at the switching point from the other side to the one side, there is a difference between the torques of both valve operating characteristics, so that torque variation occurs at the time of switching.

Further, when both valve operating characteristics are forcibly switched by a manual operation or the like, there is often a torque difference at this switching point, resulting in torque fluctuation.

Further, when the fuel economy-oriented driving mode is selected, the valve operating characteristics are switched at the intersection of the equal fuel consumption curves so as to be optimal for low fuel consumption traveling, but the torque does not match at this intersection, and therefore the torque fluctuation is caused. Often occurs.

In view of the above problems, it is an object of the present invention to propose a method of controlling engine torque that can reduce shock at the time of switching.

B. Configuration of the Invention (Means for Solving the Problem) In order to solve the above problems, the first aspect of the present invention
In the control method of (1), it is detected whether or not the switching condition of the valve operating characteristic is satisfied, and when the switching condition is satisfied, the expected switching torque after switching is calculated based on the switching condition,
The engine torque is corrected so as to gradually approach the expected switching torque while maintaining the valve operating characteristics used until the establishment of the switching condition is detected, and when the engine torque matches the expected switching torque, the above switching is performed. At the same time as switching is performed based on the conditions, the above correction is canceled.

In the second control method, it is detected whether or not a switching condition is satisfied for the valve operating characteristic, and when the switching condition is satisfied, an expected switching torque after switching is calculated based on the switching condition to determine the valve operating characteristic. Simultaneously with the switching, the engine torque after the switching is corrected to match the engine torque before the switching, and the engine torque is gradually brought close to the expected switching torque.

(Operation) When the first control method is used, if there is a torque difference before and after the switching of the valve operating characteristics, the engine torque is corrected by controlling the fuel injection amount of the engine, adjusting the ignition timing, etc. before the switching. Then, the torque difference is gradually reduced, and when the torque difference disappears, the valve operating characteristic is switched and the correction is canceled. As a result, the torque difference is gradually reduced, and smooth switching is performed without sudden torque fluctuations.

Further, if the second control method is used, the engine torque is corrected so that the torque difference is zero and the valve operating characteristic is switched at the same time, and then the correction amount of the engine torque is gradually returned to zero. Be done. As a result, when the valve operating characteristics are switched, torque fluctuation does not occur, the torque difference is gradually reduced, and smooth switching is performed.

(Examples) Hereinafter, preferred examples of the present invention will be described with reference to the drawings.

First, the variable valve timing / lift mechanism VT will be described with reference to FIGS. 1 and 2. A pair of intake valves 1a, 1b are provided for each mechanism of the engine E, and the pair of intake valves 1a, 1b are provided on a camshaft 2 driven at a rotation ratio of 1/2 in synchronization with the rotation of the engine. A first low speed cam 3, a second low speed cam 3'and a high speed cam 5 which are integrally provided, and first, second and third rocker arms pivotally supported by a rocker shaft 6 parallel to the cam shaft 2. It is opened and closed by the action of 7,8,9.

The camshaft 2 is rotatably arranged above the engine body, and the first low speed cam 3 is integrally provided on the camshaft 2 at a position corresponding to one intake valve 1a. 3'is integrally provided on the camshaft 2 at a position corresponding to the other intake valve 1b. Further, the high speed cam 5 is integrally provided on the cam shaft 2 at a position corresponding to between the intake valves 1a and 1b. Moreover, the first low-speed cam 3 has a shape corresponding to the low-speed operation of the engine, and has the high-level portion 3a having a relatively small amount of outward projection along the radial direction of the camshaft 2. Further, the high speed cam 5 has a shape corresponding to the high speed operation of the engine, and the amount of protrusion of the cam shaft 2 outward in the radial direction is made larger than that of the high-order portion 3a of the first low speed cam 3, and It has a high-order portion 5a that covers a wider central angle range than the high-order portion 3a. Further, the second low speed cam 3'also has a shape corresponding to the low speed operation of the engine, and has a high portion 3a 'having a relatively small outward protrusion amount along the radial direction of the camshaft 2. This high-order part 3a 'is smaller than the high-order part 3a.

The rocker shaft 6 is fixedly arranged below the cam shaft 2. First to third rocker arms 7 to 9 are pivotally supported on the rocker shaft 6, respectively, but the first and second rocker arms 7 and 8 are basically formed in the same shape.
That is, the bases of the first and second rocker arms 7 and 8 are pivotally supported by the rocker shaft 6 at positions corresponding to the intake valves 1a and 1b, and extend to positions above the intake valves 1a and 1b. Set up. Further, a cam slipper 10 slidingly contacting the low speed cam 3 is provided above the first rocker arm 7, and a cam slipper 11 capable of abutting the second low speed cam 4 is provided above the second rocker arm 8. In the first and second rocker arms 7 and 8, tappet screws 12 and 13 that can come into contact with the upper ends of the intake valves 1a and 1b are screwed to the ends of the intake valves 1a and 1b located above the intake valves 1a and 1b, respectively. To be done.

On the other hand, flanges 14 and 15 are provided above the intake valves 1a and 1b, and a valve spring 16 surrounding the intake valves 1a and 1b is provided between the flanges 14 and 15 and the engine body. 17 are installed, and the valve springs 16 and 17 allow the intake valves 1a and 1b to be installed.
Is biased in the valve closing direction, that is, upward.

Further, as also shown in FIG. 3, the third rocker arm 9 is pivotally supported on the rocker shaft 6 between the first and second rocker arms 7 and 8. The third rocker arm 9 is slightly extended from the rocker shaft 6 toward the intake valves 1a, 1b, and a cam slipper 18 slidingly contacting the high speed cam 5 is provided on the upper portion thereof. A bottomed cylindrical lifter 19 is in contact with the lower surface of the end portion of the third rocker arm 9, and the lifter 19 is provided between the lifter spring 20 and the engine body.
Is urged upward by. As a result, the cam slipper 18 of the third rocker arm 9 is always in sliding contact with the high speed cam 5.

As shown in FIG. 4, first to third rocker arms 7,8,9
Are in sliding contact with each other, and the connecting means 21 capable of switching between a state in which the relative angular displacements thereof are possible and a state in which the respective rocker arms 7 to 9 are integrally connected are the first and second rocker arms 7. , 8,9.

The connecting means 21 connects the first and third rocker arms 7 and 9 and the position that connects the first and second rocker arms 9 and 8 and the third piston 2 and the second rocker arms 9 and 8 which are movable between the positions where the connection is released. The second piston 23 movable between the positions for releasing the connection and the first and second pistons 22, 23
24 for restricting the movement of the stopper 24 and the stopper 24 for moving the first and second pistons 22, 23 to the connection release position side.
And a spring 25 for urging.

The first rocker arm 7 is provided with a first guide hole 26 that opens toward the third rocker arm 9 side and is parallel to the rocker shaft 6, and a step portion 27 is formed at the bottom of the first guide hole 26. The small diameter portion 28 is provided via the. The first piston 22 is slidably fitted in the first guide hole 26, thereby defining a hydraulic chamber 29 between the first piston 22 and the bottom surface of the first guide hole 26. Further, an oil passage 30 communicating with the hydraulic chamber 29 is provided in the first rocker arm 7, and an oil passage 31 communicating with a hydraulic supply source (not shown) is provided in the rocker shaft 6. Further, the two oil passages 30 and 31 are always communicated with each other via the communication hole 32 formed in the side wall of the rocker shaft 6 regardless of the rocking state of the first rocker arm 7.

The axial length of the first piston 22 is such that, when one end of the first piston 22 comes into contact with the step portion 27, the other end does not project from the side surface of the first rocker arm 7 facing the third rocker arm 9 side to the third rocker arm 9 side. Is set to. A spring 33 having a smaller spring force than the spring 25 is interposed between the bottom of the first guide hole 26 and the first piston 22.

A guide hole 34 corresponding to the first guide hole 26 of the first rocker arm 7 is formed in the third rocker arm 9 between both side surfaces, and the guide hole 34 has a length corresponding to the entire length of the guide hole 34. The second piston 23 having a thickness is slidably engaged.
Moreover, the outer diameter of the second piston 23 is set to be the same as that of the first piston 22.

In the second rocker arm 8, corresponding to the guide hole 34,
The second guide hole 35 opened toward the third rocker arm 9 side
Is provided, and the disk-shaped stopper 24 is inserted into the second guide hole 35.
Are slid together. A regulation step 36 is provided on the bottom side of the second guide hole 35.
The small diameter portion 37 is provided through the second guide hole 35.
The second rocker arm 8 between the bottom of the
Has a small diameter insertion hole 38 concentric with the second guide hole 35, and a small diameter guide rod 39 provided integrally with the stopper 24 and concentric with the second guide hole 35 is inserted into the insertion hole 38. Further, a coil-shaped spring 25 surrounding the guide rod 39 is interposed between the stopper 24 and the bottom of the second guide hole 35.

Next, the variable valve timing /
The operation of the lift mechanism VT will be described.

When the engine E is operating at low speed, the hydraulic chamber of the connection switching means 21
The hydraulic pressure is not supplied to 29, and the stopper 24 is pressed toward the third rocker arm 9 side by the spring 25.
22 moves through the second piston 23 until it comes into contact with the step 27. In this state, the contact surfaces of the first piston 22 and the second piston 23 are at positions corresponding to the sliding contact surfaces of the first and third rocker arms 7 and 9, and the contact surfaces of the second piston 23 and the stopper 24. Is at a position corresponding to the sliding contact surfaces of the third rocker arm 7 and the second rocker arm 8. Therefore, the first to third rocker arms 7,8,9 are connected to the first and second rocker arms.
Pistons 22 and 23 and second piston 23 and stopper 2
Relative angular displacement is possible by sliding each 4 together.

When the connection switching means 21 is in the connection released state, the rotation operation of the cam shaft 2 causes the first rocker arm 7 to swing in response to the sliding contact with the first low speed cam 3, and the second rocker arm 8 to move. It swings in accordance with the sliding contact with the second low speed cam 3 '. Therefore, both intake valves 1a, 1b are opened and closed by the first and second low speed cams 3, 3 '. At this time,
The third rocker arm 9 swings due to the sliding contact with the high speed cam 5, but the swinging motion has no effect on the operation of both intake valves 1a, 1b.

Thus, during low speed operation of the engine E, one intake valve 1a opens and closes at a timing and lift amount corresponding to the shape of the first low speed cam 3 as shown by the broken line 3 and the alternate long and short dash line 3'in FIG. 6A. Activates the other intake valve 1b
Opens and closes at a timing and lift amount according to the shape of the second low speed cam 3 '. Therefore, an air-fuel mixture inflow speed suitable for low speed operation can be obtained, fuel consumption can be reduced and kicking can be prevented, and optimum low speed operation can be performed.

In order to obtain an air-fuel mixture inflow speed suitable for low-speed operation,
For example, as shown in FIG. 6B, the high position portion 3a 'of the second low speed cam 3'may be lowered so that the opening time / amount of the intake valve 1b during the low speed operation becomes very small.
The high valve 3a 'is set to zero and the intake valve is operated during low speed operation.
The valve rest state may be created by not opening 1b at all.

When the engine E is operating at high speed, the hydraulic pressure is supplied to the hydraulic chamber 29 of the connection switching means 21. As a result, as shown in FIG. 5, the first piston 22 moves toward the third rocker arm 9 side against the spring force of the spring 25, and the second piston 23 moves to the first
It is pushed by the piston 22 and moves to the second rocker arm 8 side. As a result, the first and second pistons 22 and 23 move until the stopper 24 comes into contact with the regulation step portion 36, the first and third rocker arms 7 and 9 are connected by the first piston 22, and the second piston 23 By the 3rd and 2nd rocker arms
9,8 are connected.

In this way, in the state where the first to third rocker arms 7, 8 and 9 are connected to each other by the connection switching means 21, the swing amount of the third rocker arm 9 slidingly contacting the high speed cam 5 is the largest, The first and second rocker arms 7 and 8 swing together with the third rocker arm 9. Therefore, as shown by the solid line 5 in FIG. 6A, both intake valves 1a and 1b are opened and closed at the timing and lift amount according to the shape of the high speed cam 5. In this case, the timing and the lift amount are larger than those during low speed operation, and intake air suitable for high speed operation can be obtained, so that the engine output can be improved.

In the above operation, the first and second low speed cams
The opening / closing timing and lift amount of the intake valves 1a, 1b based on 3, 3'are referred to as the low speed valve operating characteristic, and the opening / closing timing and lift amount of the intake valves 1a, 1b based on the high speed cam 5 are referred to as the high speed valve operating characteristic. Both valve operating characteristics are used by dividing into a low speed operation area and a high speed operation area,
The relationship between the engine output torque and the engine speed at this time is as shown in FIG. As can be seen from this figure, the maximum output torque T _L in the low speed valve operation characteristic operation is smaller than the maximum output torque T _H in the high speed valve operation characteristic operation.

FIG. 8 shows a configuration of an engine having the above valve operating characteristic switching mechanism, which uses the engine torque control method according to the present invention.

In the upper part of the engine body 41, the intake passage 42 and the intake passage
A variable valve timing lift mechanism VT for opening and closing 42 is provided. To the oil passage 31 (see FIGS. 4 and 5) in this mechanism, pressure oil controlled by the solenoid valve 60 and a switching valve (not shown) is supplied through the oil passage 61. An air cleaner 44 is attached to the suction port of the suction passage 42.
From the side closer to the air cleaner 44, the throttle valve 45
An intake air temperature sensor 52 for detecting the intake air temperature TA and an injector 46 are arranged near the engine.

Further, an exhaust passage 43 is attached to the engine body 41,
In the middle of that, an O ₂ sensor 53 that detects the oxygen concentration O ₂ in the exhaust gas
Is provided.

Further, a spark plug 47 is attached to the upper part of the engine body 41.

Near the throttle valve 45, a throttle position sensor 51 that detects the throttle opening θth and an intake negative pressure
The pressure sensor 54 for detecting P _B is connected, and these sensors and the intake air temperature sensor 52 send a signal representing the state of intake air to the electronic control circuit 48.

Further, a signal representing the cooling water temperature TW is sent from the engine speed Ne, the vehicle speed V and the water temperature sensor 55 to the electronic control circuit 48.

Based on these signals, the electronic control circuit 48 grasps the traveling state, sends a switching signal VTS to the solenoid 60a in the solenoid valve 60, and operates the solenoid valve 60. Solenoid valve 60 operates and oil passage
It is confirmed that when the pressure oil flows into the inside of the valve 31, the high speed valve operating characteristic is switched and the hydraulic switch 50 is turned on to switch the valve operating characteristic.

Further, from the electronic control circuit 48, a signal for controlling the fuel injection amount of the injector 46 and the ignition timing of the spark plug 47,
Sent to each.

FIG. 9 and FIG. 10 are a flow chart of the engine torque control method according to the present application and claim 1, and a series of graphs showing the concept of operation step by step in an easy-to-understand manner.

First, the switching process from the high speed valve operating characteristic to the low speed valve operating characteristic will be described with reference to the flowchart of FIG. 9 and the graph (a) of FIG.

If it is determined in step S1 that the switching condition set in the electronic control circuit 48 based on the information sent from each sensor in FIG. In step S2, 1 is set in the flag F _VT which is a signal to start the engine torque correction. Next, when it is confirmed in step S4 that the high speed valve operation characteristic HVT is switched to the low speed valve operation characteristic LVT, the process proceeds to step S5.

Graph (a-1), shows the variation of the engine torque T _ENG in the case of performing (under normal operation in) the valve operating characteristic changeover without correcting the engine output, the engine torque T _ENG The corrections described below are added.

In step S5, based on the above switching conditions, the engine torque expected to be generated by the engine under normal operation after switching to the low speed valve operating characteristic is calculated, and this is set as the expected switching torque (low speed) T _FL , and the correction torque is calculated. Set the target value. Next, in step S6, the corrected engine torque _T'ENG
And it is judged whether the expected switching torque (low speed) T _FL is equal, but in the first routine, the engine torque has not been corrected yet, so T ′ _ENG ≠ T _FL ,
The process proceeds to step S7 as it is. In step S7, in order to reduce the engine torque T _HVT in the high-speed valve operating characteristic before the switching, which is the current engine torque, by a predetermined amount so as to approach the expected switching torque (low speed) T _FL , the ink jet 46 in FIG. The fuel injection amount from is reduced, and the air-fuel ratio A / F is made thin (lean) to perform correction.

Above steps S1, S2, S4 to S7 is a process from switching condition satisfied until the engine torque correction start, shown in the graph (a) at time t _1.

After this, when the first routine is completed after passing through step S21, the procedure returns to step S1 again to enter the second routine. Here, since the switching condition has already been established, the routine proceeds to step S3, where the fact that the engine torque is being corrected is flag _FVT = 1 set in step S2 for the first time.
Then, the process proceeds to step S5 through step S4. Step S5
Then, of course, the engine torque T _LVT after switching to the low speed valve operability also changes slightly depending on the running state that changes from moment to moment, so the expected switching torque (low speed) should be adjusted accordingly.
Calculate T _FL anew and correct the one calculated in the first routine. Thus, after that, the correction is performed while correcting the expected switching torque (low speed) T _FL for each routine, but this switching time is short and the amount of change in torque is very small. ), The expected switching torque (low speed) T _FL is constant. Since the amount of change in torque within the switching time is small in this way, the initial predicted switching torque (low speed) T _FL may be used without modification.

Next, in step S6, if the engine torque T ′ _ENG (T ′ _HVT ) corrected in the first routine is larger than the expected switching torque (low speed) T _FL , the air-fuel ratio A / F is made leaner, The corrected engine torque T '
_ENG (T ' _HVT ) is lowered again by a predetermined amount.

In this way, while the routine of steps S1, S3, S4 to S7 and S21 is repeated, the correction amount that the engine torque T _ENG (T _HVT ) of the high speed valve operating characteristic under normal operation receives is the graph (a-2). As shown in, it gradually increases toward the negative side. As a result, the corrected engine torque T '
_ENG (T ' _HVT ) gradually approaches the predicted switching torque (low speed) T _FL as shown in the graph (a-3).

Then, the corrected engine torque T ′ _ENG (T ′ _HVT )
When it is determined in step S6 that the estimated switching torque (low speed) T _FL has become equal, the process proceeds to step S8, and the flag F _{VT is set} to 0 so as to signal the end of engine torque correction.
And

Further, in step S9, the switching signal VTS is sent to the solenoid 60 in FIG. 8 to operate the solenoid valve 60, and the pressure oil is sent to the oil passage 31 in the variable valve timing / lift mechanism VT. In this way, the switching from the high speed valve operation characteristic HVT to the low speed valve operation characteristic LVT is executed. At the same time, in step S8, the correction of the engine torque T _ENG is released in step S20, the air-fuel ratio A / F is returned to the normal value, and the engine is returned to the normal operating state. This process is time on graph (a)
indicated by t ₂ . In this way, the switching process from the high speed valve operation characteristic HVT to the low speed valve operation characteristic LVT is completed.

On the other hand, low-speed valve operating characteristic LVT to high-speed valve operating characteristic H
In the case of switching to VT, in the first routine, steps S1 and S2 are performed in the same manner as in the above switching, and the process proceeds from step S4 to step S15.

The graph (b-1) shows a change in the engine torque T _ENG when the valve operation characteristics are switched under normal operation, and the correction described below is added to the engine torque T _ENG. .

In step S15, it calculates an engine torque that is expected engine occurs in normal operation under after switching to high-speed valve operating characteristic HVT, which was the expected switching torque (fast) T _FH, a target value of the correction.

From step S16, in the first routine, similarly to the switching from the high speed valve operation characteristic to the low speed valve operation characteristic, the process directly proceeds from step S16 to step S17. Step S1
In 7, in order to increase the engine torque T _LVT in the low speed valve operating characteristic before switching, which is the current engine torque, by a predetermined amount so as to approach the expected switching torque (high speed) T _FH ,
The fuel injection amount from the injector 46 in FIG. 8 is increased,
The air-fuel ratio A / F is made thicker (enriched) for correction, and the first routine is ended.

In the series of graphs (b) this process is shown at time t ₃ .

In the second and subsequent routines, through steps S1, S3, S4,
Go to step S15.

In step S15, similarly to step S5, the expected switching torque (high speed) T _FH is newly calculated for each routine. However, in the graph (b), similarly to the graph (a), the expected switching torque (high speed) T _FH is constant.

Next, in step S16, the engine torque T '
_{If ENG} (T ' _LVT ) is smaller than the expected switching torque (high speed) T _FH , the air-fuel ratio A / F is further enriched and the engine torque is increased again by a predetermined amount.

As described above, while Steps S1, S3, S4, S15 to S17 and S21 are repeated, the correction amount that the engine torque T _ENG (T _LVT ) of the low speed valve operation characteristic under normal operation receives is shown in the graph (b-2). As shown, it gradually increases toward the plus side. As a result, the corrected engine torque T '
_As shown in the graph (b-3), _ENG (T ' _LVT ) gradually approaches the predicted switching torque (high speed) T _FH .

Finally, when it is determined in step S16 that the engine torque _T'ENG (T ' _LVT ) and the expected switching torque (high speed) _TFH are equal, the process proceeds to step S18.
The flag _{FVT is set} to 0 so as to signal the end of engine torque correction.

Further, the process proceeds to step S19, the solenoid 60a in FIG.
The switching signal VTS sent to the control valve is cut, and the supply of pressure oil from the solenoid valve 60 to the variable valve timing / lift mechanism VT is stopped. In this way, the switching from the low speed valve operation characteristic LVT to the high speed valve operation characteristic HVT is executed. At the same time, in step S20, the correction of the engine torque T _ENG is released and the engine is returned to the normal operating state. This process is shown at time t ₄ in graph (b). Thus, the switching process from the low speed valve operation characteristic LVT to the high speed valve operation characteristic HVT is completed.

As described above, when this control method is used, the engine torque of the engine is generated after switching as shown in the graphs (a-3) and (b-3) while maintaining the valve operating characteristics before switching. Then, it is corrected to gradually approach the expected switching torque, and when both match, the valve operating characteristics are switched and this correction is released and the engine is returned to the normal operating state, so there is no sudden torque fluctuation. It is possible to switch, and it is possible to prevent a shock due to switching of valve operating characteristics.

Incidentally, in the above description, in step S7 and step S17, the correcting means of the engine torque T _ENG, the air-fuel ratio A /
Although the lean or rich F is used, other means, for example, the ignition timing can be changed or the throttle opening can be operated.

However, regarding the switching from the low speed valve operation characteristic to the high speed valve operation characteristic in the present control method, for example, the engine torque when the air-fuel ratio A / F of the engine operating with the low speed valve operation characteristic is most enriched, The engine torque that can be corrected and generated in the low speed valve operation characteristic is equal to the engine torque in the high speed valve operation characteristic under normal operation, as in the case where the engine torque is larger than the engine torque generated in the high speed valve operation characteristic. Effective only when it exceeds.

FIG. 11 and FIG. 12 are a flowchart and a series of graphs showing the concept of operation step by step in an easy-to-understand manner of the engine torque control method according to claim 2 of the present application.

First, the switching process from the high speed valve operating characteristic to the low speed valve operating characteristic will be described with reference to the flowchart of FIG. 11 and the graph (c) of FIG.

When it is determined in step S31 that the switching condition set according to the traveling state at that time is established, step S32
Then, 1 is set in the flag F _VT so as to signal the start of the engine torque correction. Next, in step S34, when it is confirmed that the high speed valve operation characteristic HVT is switched to the low speed valve operation characteristic LVT, the process proceeds to step S35.

The graph (c-1) shows a change in the engine torque T _ENG when the valve operating characteristic is switched (under normal operation without correcting the engine output).
_{ENG The} following corrections are added.

In step S35, the engine torque expected to be generated by the engine under the normal operation after the switching to the low speed valve operation characteristic LVT is calculated based on the switching condition, and is set as the expected switching torque (low speed) T _FL .

Next, in step S36, since the flag F _VT was 0 in the previous routine (when the switching condition is not satisfied), this time is the first routine, that is, the valve operating characteristic is still switched. If it is confirmed that there is no such change, the valve operating characteristic is switched in the next step S37. At the same time, in step S38, the expected switching torque (low speed) T _FL calculated in step S35 is used as a reference value, and the engine output _sufficient to match the engine torque T _HVT in the high-speed valve operating characteristic before switching is set. Make a correction. Here, a means for making the air-fuel ratio A / F rich at once is used.

When the valve operating characteristics are switched in step S37, the engine torque T _ENG decreases to T _LVT as shown in the graph (c-1), but this torque decrease is offset by the engine torque increase correction in step S38. Therefore, there is no change in engine torque at this point.

Up to this point (steps S31, S32, and S34 to S38) is the process from the establishment of the switching condition to the valve operation characteristic switching and the engine torque correction start, and in the series of graphs (c),
Indicated at time t ₁ .

When the first routine ends after step S62, the process returns to step S31. Here, since the switching condition has already been established, the routine proceeds to step S33, where it is judged that the engine torque is being corrected by the flag F _VT = 1 at step S32 of the first time, and step S34 is followed by step S35. Go to.

In step S35, according to the running state that changes from moment to moment,
The expected switching torque (low speed) T _FL is newly calculated, and the one calculated in the first routine is corrected.

Next, in step S36, the flag F _VT was determined in the previous routine.
= 0, that is, it is confirmed that the valve operating characteristic has already been switched, and the process proceeds to step S39. In step S39, correction (increase) in the first routine
Engine torque _{T'ENG at the specified} low speed valve operating characteristics
If (T ′ _LVT ) is larger than the newly calculated expected switching torque (low speed) T _FL , the corrected engine torque T ′ _ENG (T ′ _LVT ) is changed to the expected switching torque (low speed) in step S40. ) To reduce the air-fuel ratio A / F by a predetermined amount so as to approach T _FL , the air-fuel ratio A / F is made thinner (lean) than the air-fuel ratio A / F determined in the first routine for correction.
That is, the correction amount of the air-fuel ratio A / F corrected to the rich side is corrected to the original value.

In addition, gradually become lean in the third and subsequent routines,
As shown in the graph (c-2), the correction amount is brought close to zero,
Gradually return to normal operation.

In this way, steps S31, S33 to S36, S39, S40 and
While repeating the routine of S62, the engine torque T _ENG (T
_As shown in the graph (c-2), the correction amount received by the _LVT ) gradually decreases with the plus side correction amount received in the first routine being the maximum. As a result, the corrected engine torque T ′ _ENG (T ′ _LVT ) gradually approaches the predicted switching torque (low speed) T _FL as shown in the graph (c-3).

Then, when it is finally determined in step S39 that the engine torque _T'ENG (T ' _LVT ) and the expected switching torque (low speed) T _FL are equal, the process proceeds to step S61,
Flag F to signal the end of engine torque correction.
_{Set VT} = 0. This process is shown at time t ₂ in graph (c). Thus, the switching process from the high speed valve operation characteristic HVT to the low speed valve operation characteristic LVT is completed.

On the other hand, low-speed valve operating characteristic LVT to high-speed valve operating characteristic H
In the case of switching to VT, in the first routine, similarly to the above switching, through steps S31 and S32, step S34
To Step S55.

Graph (d-1), in the case of performing the valve operating characteristic switching under normal operation, shows the change of the engine torque T _ENG, correction to be described below in the engine torque T _ENG is Kuwawae .

In step S55, the engine torque expected to be generated by the engine under normal operation after switching to the high speed valve operating characteristic HVT is calculated, and this is set as the predicted switching torque (high speed) T _FH .

Next, from step S56, similarly to step S36 in the first routine, the process proceeds to step S57 to switch the valve operating characteristics. At the same time, in step S58, the expected switching torque (high speed) T _FH calculated in step S55 is used as a reference value, and this can be matched with the engine torque T _ENG (T _LVT ) in the low speed valve operating characteristic before switching. Of the engine torque T _ENG (T _HVT ) after switching
In addition, reduce this. Here, the air-fuel ratio A / F is corrected by a means for making it leaner at once. In the series of graphs (d), this process is shown at time t ₃ .

After this, through step S62, the first routine ends.

In the second routine, as in the case of the above switching, step S3
1, proceeds to S33, S34 and step S55.

In step S55, the predicted switching torque (high speed) T _FH is newly calculated for each routine, as in step S35.

From the next step S56, similarly to step S36, the process proceeds to step S59.

If the engine torque T ′ _ENG (T ′ _HVT ) corrected in the previous routine is smaller than the newly calculated expected switching torque (high speed) T _{FH in} step S59, step S59 is executed.
At 60, the corrected engine torque T '
_ENG (T ' _HVT ), this time predicted switching torque (high speed) T _FH
The air-fuel ratio A / F is enriched so that it approaches

Further, in the third and subsequent routines, the richness is gradually increased, and eventually the normal operation state is restored.

In this way, steps S31, S33, S34, S55, S56, S59, S6
While the routines of 0 and S62 are repeated, the correction amount that the engine torque T _ENG (T _HVT ) under normal operation receives is the graph (d
As shown in -2), the minus side correction amount received in the first routine is maximized, and gradually becomes smaller. As a result, the corrected engine torque T ′ _ENG (T ′ _HVT ) is
As shown in the graph (d-3), the predicted switching torque (high speed) T _FH gradually approaches.

At last step S59, the engine torque _{T 'ENG (T' HVT)} , when the expected switching torque (fast) T _FH is determined to have become equal to 0 to Urafu F _VT at step S61 is set. Thus, the switching process from the low speed valve operation characteristic LVT to the high speed valve operation characteristic HVT is completed.

As described above, if this control method is used, the expected switching torque expected to be generated by the engine operating normally with the valve operating characteristics after switching is calculated, and the estimated switching torque and the engine before switching the valve operating characteristics are calculated. A correction amount corresponding to the difference from the torque is added to the engine torque after switching the valve operating characteristics, and thereafter, the engine is returned to the normal operating state so that the corrected engine torque gradually approaches the predicted switching torque. Switching can be performed without causing torque fluctuation, and a shock due to switching of valve operating characteristics can be prevented.

Incidentally, in the above description, in step S40 and step S60, the correcting means of the engine torque T _ENG, the air-fuel ratio A /
Although enrichment or leaning of F is used, other means such as changing the ignition timing or manipulating the throttle opening can be used.

However, when switching from the high-speed valve operating characteristic to the low-speed valve operating characteristic in this control method, for example, the engine torque when the air-fuel ratio A / F of the engine operating with the low-speed valve operating characteristic is maximized is the high-speed valve operating characteristic. When the engine torque that can be corrected and generated in the low speed valve operating characteristic exceeds the engine torque under normal operation in the high speed valve operating characteristic, such as when the engine torque is larger than the engine torque generated in the operating characteristic. Only valid for.

C. As described above, according to the present invention, even when there is a difference in engine torque before and after the switching of the valve operating characteristics, the engine output is controlled so that the engine torque before switching gradually approaches the engine torque after switching. Compensate and switch when both match and cancel the compensation at the same time to return the engine to the normal operating state, or at the same time as switching, match the engine torque after switching to the engine torque before switching The engine output correction is performed so that the correction is gradually canceled and the engine is gradually returned to the normal operating state.Therefore, the valve operating characteristic can be switched without a sudden torque fluctuation. Shock can be prevented.

[Brief description of drawings]

1 and 3 are side cross-sectional views showing the valve periphery of the valve operating characteristic switching mechanism, FIG. 2 is a top view showing the valve periphery, and FIGS. 4 and 5 are the valve components. FIG. 6A and FIG. 6B are cross-sectional top views showing the rocker arm coupling means of the operating characteristic switching mechanism, FIGS. 6A and 6B are graphs showing the change in the intake and exhaust steps of the valve and the lift amount, and FIG. FIG. 8 is a graph showing the relationship between the rotational speed and the torque of an engine having a valve operating characteristic switching mechanism, FIG. 8 is a schematic diagram showing the configuration of an engine having the valve operating characteristic switching mechanism, and FIG. FIG. 10 is a flowchart showing an engine torque control method according to the invention of Item 1, FIG. 10 is a graph showing changes in engine torque before and after switching of valve operating characteristics using the above control method, and FIG. FIG. 12 is a flowchart showing an engine torque control method according to the invention of claim 2, and FIG. 12 is a graph showing changes in engine torque before and after switching of valve operating characteristics using the above control method. 1 ... Intake valve, 2 ... Camshaft 6 ... Rocker shaft, 7-9 ... Rocker arm 41 ... Engine body, 46 ... Injector 47 ... Spark plug, 48 ... Electronic control circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Kinma 1-4-1, Chuo, Wako-shi, Saitama Inside of Honda R & D Co., Ltd. (72) Inventor Junichi Miyake 1-4-4, Chuo, Wako, Saitama No. 1 inside Honda R & D Co., Ltd. (72) Inventor Atsushi Kato 1-4-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd.

Claims (2)

[Claims] 1. An engine in which the valve operating characteristics of at least one of an intake valve and an exhaust valve are switchable, and it is detected whether or not a switching condition of the valve operating characteristics is satisfied, and it is detected that the switching condition is satisfied. At this time, an expected switching torque generated when the valve operating characteristic is switched based on this switching condition is calculated, and the valve operating characteristic used until the establishment of the switching condition is detected, The engine torque is corrected so as to gradually approach the predicted switching torque, and when the engine torque matches the predicted switching torque, the valve operation characteristic is switched based on the switching condition, and at the same time, the correction is released. An engine torque control method at the time of switching valve operating characteristics. 2. An engine in which the valve operating characteristics of at least one of an intake valve and an exhaust valve are switchable, and it is detected whether or not the switching condition is satisfied, and when the satisfaction of the switching condition is detected, the switching is performed. The expected switching torque generated when the valve operating characteristic is switched based on the condition is calculated, and at the same time the valve operating characteristic is switched from one to the other, the engine torque is corrected to match the engine torque before switching. Then, the engine torque control method at the time of switching the valve operation characteristic is characterized in that the engine torque is gradually brought close to the predicted switching torque.