JPH04179837A - Variable valve system for internal combustion engine - Google Patents

Abstract

PURPOSE:To correctly synchronize the output correction control for absorbing a torque shock following a cam change-over, by generating an output change- over signal so that the cam change-over may terminate with a certain period of time before a target cylinder starts it intake stroke. CONSTITUTION:When a cam change-over judging means 68 judges the change- over of a cam in response to the operational state detected by an operational- state detector 67, an estimated crank angle calculator 69 calculates a crank angle position determined by estimating a change-over delay time length with respect to the present crank angle position. Further, a change-over angle calculator 71 calculates a change-over angle so that an actual change-over may terminate at a substantially intermediate point between a starting point of a certain cylinder intake stroke and a starting point of a target cylinder intake stroke. As a result, actual change-over of a cam is terminated before doing its intake stroke even when response delay is varied. Accordingly, since output correction by an output correction control means 65 is started at this specific cylinder, torque difference at the time of change-over can reliably be absorbed.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a variable valve device for an internal combustion engine that switches cams depending on operating conditions.

(Prior Art) A valve train that drives intake and exhaust valves of an internal combustion engine is set to obtain optimal valve timing in accordance with the output characteristics required by the engine.

However, this required valve timing differs depending on the operating conditions of the engine. For example, in a low load range, both the valve lift and valve opening period are small, whereas in a high load range, a large valve lift and valve opening period are required. Engines that operate under a wide range of conditions, such as automobile internal combustion engines,
It is quite difficult to set the valve timing for which operating range, and in any case, it is not possible to achieve optimal matching under all operating conditions.

Therefore, as described in Japanese Patent Application Laid-open No. 63-167016, by providing a plurality of cams with different cam characteristics (cam profiles) and switching the cams depending on the operating conditions, the optimum valve timing can be achieved for each cam. A variable valve device has been proposed that allows the operation of the vehicle.

This system switches between a low-speed cam that has high torque characteristics in the low-speed range and a high-speed cam that has high torque characteristics in the high-speed range, depending on the operating conditions. This is what we are trying to do.

(Problem to be Solved by the Invention) By the way, the above-mentioned cam switching is performed at a rotational speed at which the output is the same at the same throttle opening so that the output does not change discontinuously before and after the switching. The cams selected are two output cams with characteristics that emphasize output (torque) in the low and high rotation ranges, and a fuel efficiency cam that emphasizes fuel efficiency in the partial load range. of,
When equipped with three cams, switching from the fuel efficiency cam to the output cam (or vice versa) requires the same throttle opening before and after switching, since the torque generated by the fuel efficiency cam is relatively low. If you try to maintain this, the torque difference will become very large.

In other words, to switch from a low-speed output cam to a high-speed output cam, you just need to switch at the rotation speed that produces the same output as described above, but in the case of a fuel efficiency cam, the output is output at the same throttle opening. Because the torques do not match, a large torque difference occurs during switching.

Switching from the fuel consumption cam to the output cam is done by switching to a low-speed output cam in the low-speed range and a high-speed output cam in the high-speed range, but naturally the low-speed output cam is faster in the low-speed range. The generated torque is larger than that of the type output cam, and the opposite is true in the high rotation range, so no matter which rotation range the switching is performed, a large torque step will occur.

Note that switching to the cam is performed according to the driver's will, that is, changes in the opening degree of the accelerator pedal, etc. For example, when driving with the fuel efficiency cam, the accelerator pedal is further depressed and the output exceeds the range of the fuel economy cam. When requesting torque,
Depending on the rotation range at that time, either a low speed type or a high speed type output cam is selected and switched.

Therefore, in order to absorb the large torque difference that occurs before and after such switching, the throttle valve is separated from the accelerator pedal and the opening can be controlled independently. By automatically correcting throttle opening, ignition timing, etc. as necessary to absorb the torque difference determined from Since the output torque increases rapidly if the throttle opening remains unchanged, the throttle valve opening is reduced and the ignition timing is temporarily retarded.

Incidentally, these correction controls need to be executed at the time when the cams are actually switched, and if corrections are performed before or after switching, a large switching shock will occur instead.

Cam switching is performed simultaneously on all cylinders by selectively connecting rocker arms that respond to each cam using hydraulic pressure, but if the cylinders are already in the cam lift range at the time of switching, even if hydraulic pressure is applied, Since switching is not possible during that process,
Actual switching will be delayed until the next stroke.

However, conventionally, switching was confirmed by detecting the hydraulic pressure acting on the hydraulic piston, so even when switching is delayed, output correction control is executed, which means that cam switching and output If the correction control is not synchronized and, for example, when switching from a fuel efficiency cam with a large torque difference to an output cam, the cylinder that is in the middle of the intake stroke and is still using the fuel efficiency cam will not need the same throttle opening as before. Despite this, the throttle opening is suddenly reduced and the ignition timing is significantly retarded, resulting in unstable combustion in the cylinders and misfires.

If the output correction control is not completely synchronized with the actual cam switching in this way, the torque shock at the time of switching will become larger, and the drivability will be significantly deteriorated.

The present invention solves these problems by ensuring that cam switching starts from the target cylinder determined by the crank angle position at that time, and by correctly synchronizing output correction control. .

(Means for Solving the Problems) As shown in FIG. The high-speed output cam 62 is set to have characteristics that improve fuel efficiency, and the fuel efficiency cam 6 is set to characteristics that result in good fuel efficiency.
3, a cam switching mechanism 64 that selectively switches these cams depending on the operating state and transmits the movement of the cam to at least one of the intake valve or the exhaust valve, and a cam switching mechanism 64 that corrects and controls the engine output in response to the cam switching signal. In a variable valve system for an internal combustion engine, a means 65 for detecting a crank angle of the engine and a means 67 for detecting an operating state are provided.
, a means 68 for determining cam switching according to the operating state, and a means 69 for calculating a crank angle position including a switching delay period in addition to the current crank angle position when determining cam switching.
means 70 for determining which cylinder is assumed to be in the intake stroke at this estimated crank angle position; If it is before the midpoint, it is the angle obtained by subtracting the estimated angle from the midpoint, and if it is after the midpoint, it is the start point of the intake stroke of the next cylinder in the firing order, and the next one. means 71 for calculating an angle obtained by subtracting an expected angle from a substantially midpoint of the starting point of the intake stroke of the cylinder as a switching angle; and means 72 for outputting a signal.

(Function) When the cam switching timing is determined, a cam switching signal is output in anticipation of the delay time of the hydraulic mechanism, etc., but this cam switching signal is generated between the start point of the intake stroke of one cylinder and the next cylinder. In anticipation of a response delay, the signal is output early so that the actual switching ends approximately at the midpoint of the start point of the intake stroke of (the target cylinder in which switching is to be started).

Therefore, even if there is some variation in response delay, the actual cam switching will definitely be completed before the target specific cylinder enters the intake stroke, and the output will be corrected from this specific cylinder accordingly. By starting the control, the torque difference at the time of switching can be reliably absorbed.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, FIGS. 2 and 3 show the specific structure of the variable valve system, which was originally published in Japanese Patent Application No. 2-117 by the present applicant.
It has already been proposed as No. 261.

21 is set to a cam profile that emphasizes fuel efficiency, and the first cam (#8 cost cam) has a small cam lift and lift section. 22 is set to a cam profile that generates high torque in a low rotation range, and the first cam is set to have a cam profile that emphasizes fuel efficiency. The second cam (low-speed output cam) has a relatively larger cam lift than 21, and 23 is set to a cam profile that generates high torque in the high rotation range.
The third cam (high-speed output cam) has a larger cam lift and lift section than the second cam 22, and these are provided in parallel on the same camshaft.

24 is an intake/exhaust valve (intake valve or exhaust valve); 25 is a main rocker arm that is in constant contact with the first cam 21 via a roller 26; 24 is opened and closed.

Two sub-rocker arms 28 and 29 that swing around the shaft 30 are supported on the main rocker arm 25 in parallel with the roller 26, and one sub-rocker arm 28 is supported by the second cam 22 and the other. The sub-rocker arm 29 contacts the third cam 23.

When these sub rocker arms 28 and 29 are not engaged with the main rocker arm 25, they are always urged by the lost motion spring 31 so as to contact the second and third cams 22 and 23, so that they are not engaged with the main rocker arm 25. moves (oscillates) independently.

In order to selectively engage these sub-rocker arms 28 and 29 with the main rocker arm 25, first, a cylindrical pin 3 is attached to the swinging portion of one of the sub-rocker arms 28.
2, this pin 32 is also attached to the main rocker arm 25.
Pins 34 are disposed coaxially with the main rocker arm so as to be able to slide freely in the direction of the camshaft, and these pins 32 and 34 are normally held in the state shown in Fig. 2 by a return spring 36. 25, but when pressure oil is introduced through the passage 40 into the hydraulic chamber 38 in which the pin 34 is housed, the pins 32 and 34 are pushed out by a predetermined amount, and the sub-rocker arm 28 is adapted to engage with the inner rocker arm 25.

The sub rocker arm 28 is integrated with the main rocker arm 25 when it is in the base circle of the first cam 21 and the second cam 22, and after integration, the sub rocker arm 28 is integrated with the main rocker arm 25. The valve timing will be changed accordingly.

In other words, due to the characteristics of the first cam 21 emphasizing fuel efficiency, the second cam 21
The cam 22 switches to a characteristic that emphasizes output in the low rotation range.

The other sub-rocker arm 29 is configured similarly, and when pressure oil is introduced into the hydraulic chamber 39 through the passage 41, the pins 35 and 33 are pushed out against the return spring 37, and the sub-rocker arm 29 engages with the main rocker arm 25, the valve timing is switched to depend on the third cam 23, which has a larger lift and lift section than the first cam 21, as described above, and increases the output in the high rotation range. The important characteristics can be obtained.

In addition, FIG. 4 shows the valve lift characteristics from the first cam 21 to the third cam 23, and the full-open output characteristics when using each cam are shown in FIG. According to this, although the generated torque is low, the fuel efficiency is good, the second cam 22 has the highest maximum torque in the low rotation range, and the third cam 23 generates less torque in the low rotation range than the second cam 22, but The maximum torque is greatest in the high rotation range.

By the way, from the first cam 21 to the second and third cams 22 and 23
A control unit 51 as shown in FIG. 6 is provided to control switching from the second and third cams 22, 23 to the first cam 21, and vice versa, to control the switching from the second and third cams 22, 23 to the first cam 21. is selected.

The control unit 51 includes a crank angle sensor 52 that detects the machine rotation speed and crank angle position, an accelerator operation amount sensor 53 that detects the operation amount of the accelerator pedal (H feed amount), and an actually selected cam position. Signals from the cam position sensor 58 are input, and based on these signals, the operation of electromagnetic valves 45 and 46, which switch the hydraulic pressure to the two hydraulic chambers 38 and 39, is controlled as will be described later.

When one solenoid valve 45 is opened, pressure oil from the oil pump is introduced into the hydraulic chamber 38 in order to operate the second cam 22.
By opening the other solenoid valve 46, the third cam 23
Pressure oil is introduced into the hydraulic chamber 39 in order to operate the engine.

By the way, the control unit 51 controls the intake air at the same time as the cam switching in order to avoid a phenomenon that causes a large torque step when switching the cams, worsens drivability due to discontinuous output fluctuations, and induces vehicle body vibration. The opening degree of the throttle valve 57 provided in the passage 58 and the ignition timing of the ignition device 59 are corrected and controlled.

The opening degree of the throttle valve 57 is increased or decreased independently of an accelerator pedal (not shown) via a servo drive circuit 55 that receives a signal from the control unit 51 and a servo motor 56 that operates based on this drive signal. The actual opening of the valve 57 is fed back to the control unit 51 via the throttle opening sensor 54. Note that the throttle valves 57 may be provided in independent intake passages for each cylinder.

When switching from the first cam 21 to the second or third cam 22, 23, the control unit 51 controls the throttle valve 57 via a servo drive circuit 55 and a servo motor 56.
The opening degree is corrected to decrease in accordance with the torque step difference from the switching target, thereby absorbing the torque increase. Also, the second
Alternatively, when switching from the third cam 22, 23 to the first cam 21, the opening degree of the throttle valve 57 is increased to perform output correction control in the direction of absorbing the torque difference.

Further, the control unit 51 simultaneously controls the ignition device 59.
By retarding the ignition timing signal for a certain period of time when switching the cam, the output is corrected and controlled in the direction of absorbing the torque difference.

The seventh section specifically shows the state of these output correction controls.
In figures (a) and (b), the former is the first cam 21 (fuel efficiency □ cam)
The latter case is when the second cam 22 is switched to the first cam 21 (low-speed output cam).

As shown in FIG. 7(a), when switching from the fuel efficiency cam to the low-speed output cam, unless the throttle opening (TVO) is changed before and after switching as shown by the solid line, the torque will increase significantly. The boost (negative suction pressure) also increases with the switching.

On the other hand, if the throttle opening is decreased by a predetermined amount as shown by the dotted line at the time of switching, and the ignition timing is temporarily retarded, the torque will remain the same as before switching, as shown by the -dotted chain line. , torque fluctuations are absorbed.

Furthermore, even if the throttle opening is reduced, the torque immediately after switching increases transiently compared to the steady state because the boost is switched from the fuel economy cam to the output cam when the boost is small, and the torque is stored in the cylinder immediately after switching. This is because the intake air amount (fuel amount) increases over time, and this is compensated for by retarding the ignition timing and lowering the output.

When switching from a low-speed output cam to a fuel efficiency cam, refer to Figure 7 (
As shown in b), if the throttle opening remains the same, the torque will decrease significantly, but by opening (increasing) the throttle opening as shown by the dotted line, it is possible to prevent the torque from dropping. To prevent further torque reduction by switching from the output cam to the fuel efficiency cam due to the strong boost just before, open the throttle in advance just before switching, and also retard the ignition timing at the same time as the torque will become too large if it continues as it is. By doing so, it is possible to prevent torque fluctuations before and after switching.

In this way, torque fluctuations can be absorbed by performing output correction control in synchronization with cam switching.
This output correction control needs to be correctly synchronized with cam switching, and moreover, when switching from the output cam to the fuel efficiency cam, it is also necessary to slightly precede the actual switching.

However, as mentioned above, since cam switching is performed using hydraulic pressure, a delay in response is unavoidable.Furthermore, all cylinders are switched simultaneously, but depending on the conditions at that time, the cam lift may already be delayed. For cylinders that are in the period,
Even if hydraulic pressure is applied, switching will not be possible. Therefore, if output correction control is executed in this state, a very large torque shock will occur because the cam is not actually switched.

Therefore, when switching the cam, it is necessary to ensure that the target cylinder is opened without delay once the switching timing is reached.By doing this, the output can be corrected to match the target cylinder. Control is also possible, and torque fluctuations can be reliably absorbed.

Therefore, in order to ensure that the cam is switched in the target cylinder, once the cam switching timing is determined, the control unit 51 takes into account the delay time, including the hydraulic system operation delay, based on the crank angle position at that time. The cylinder immediately before transitioning to the intake stroke is set as the target, and a switching signal is output to ensure switching from this target cylinder. Specifically, according to the flowchart shown in FIG. This will be explained with reference to the timing chart of FIG.

In step 1.2, the rotational speed N is read from the output of the crank angle sensor, and the accelerator opening degree Ace is read from the output of the accelerator operation amount sensor, and the cam switching timing is determined. When cam switching is determined, the crank angle θ at that time. Then, as shown in FIG. 10, a delay period t, which is preset depending on the response delay of the hydraulic system, is read (step 3,
4).

This delay period t lasts from the output of the switching signal to the solenoid valve 4.
5.46, the time t until it operates, and the time t2 from when it operates until the oil pressure starts to rise (or fall),
The setting is based on the time t3 at which the bins 32, 33, etc. actually complete the coupling or separation after the oil pressure has increased.

Next, this current crank angle θ. It is determined whether the period obtained by adding the delay period t to the above period is between consecutive cylinders in the ignition order. In other words, as shown in Fig. 9, this embodiment targets a 4-cylinder engine, and the firing order is changed from the 1st cylinder to the 4-cylinder engine.
Assuming 3rd cylinder → 4th cylinder → 2nd cylinder, in the crank angle, the midpoint between the start point of the intake stroke of the 1st cylinder and the start point of the intake stroke of the 3rd cylinder is θ1, and in the same way, Assuming that the midpoint between the start points of the intake strokes of the third and fourth cylinders is θ, hereinafter θ4 and θ2, first, in step 5, (θ.

+t) is between θ1 and θ.

If not, whether it is between the next θ and θ, and whether it is between θ4 and θ2, and furthermore, whether it is between θ2 and θ
(Step 6~
8).

If it is between θ and θ, then θ starts from the intermediate point θ4 of the next cylinder in the ignition order. The switching angle θX=θ4−(θ.

+t).

If it is between different intermediate points, calculate each θ× in the same way (steps 9 to 12).

and the crank angle position θ. When this θ and X have passed since then, the refractive angle θ=θ. When it reaches 10X, a switching signal is output (step 13.14).

Therefore, in this case, the target timing at which the switching signal is output and the pins are actually connected is always the midpoint between the specific target cylinder and the intake stroke start point of the preceding cylinder.

This is because if the coupling target point becomes the midpoint between the start point of the intake stroke of the cylinder before the target cylinder and the start point of the intake stroke of the target cylinder, variations in the response delay time of the hydraulic system will actually occur. Even if there is, switching will not be performed in the cylinder before the target cylinder, and with the highest probability, the switching will be completed before the intake stroke of the target cylinder.

Due to variations, the switching time may be delayed, but in some cases it may be earlier, and if it is too early,
The switching may end before the intake stroke start point of the cylinder one before the target cylinder, and if it is too late, the intake stroke of the target cylinder may have already started. Switching cannot be performed in the target cylinder, and switching will be performed in the next cylinder.

These things can be easily understood if we assume that the target switching end time is placed immediately before the intake stroke of the target cylinder, but in this case, the response delay time is taken into account. However, even if there is a slight deviation in the estimated time, it is conceivable that the intake stroke of the target cylinder will be immediately delayed, and in this case, of course, switching will not be possible in that cylinder.

However, in order to ensure safety, it may be possible to take into account the error caused by these response delays and advance the switching target cylinders a few more points in the ignition order. Even though the switching time has come, the switching will not be carried out for a long time, and the responsiveness to switching requests will deteriorate.

For these reasons, in order to ensure that the switching is completed in the target cylinder without delay when the switching timing is reached, the intake stroke of the shortest cylinder is determined from the current crank angle position in anticipation of the delay period. The target point at the end of switching is the midpoint between the start point of
Even before the intake stroke of the target cylinder, by replacing the next cylinder with the target cylinder, it is ensured that the cam switching is completed in the intake stroke of the target cylinder.

As a result, the switching is reliably completed during the intake stroke of the target cylinder, so the output correction control by correcting the throttle opening and ignition timing described above should be performed in synchronization with the intake stroke of the target cylinder. This makes it possible to reliably absorb output fluctuations during cam switching.

Moreover, in the target cylinder, the end of switching is aimed at approximately the midpoint of the intake stroke of the previous cylinder, so as shown in FIG. 7(b).
Even when it is necessary to start the correction control immediately before switching, such as when switching from the output cam to the fuel economy cam as shown in , it is possible to accurately carry out the correction control with a margin.

Although the above embodiment has been explained using a four-cylinder engine as an example, the present invention can naturally be applied to other engines as well.

(Effects of the Invention) As described above, according to the present invention, the switching is completed with a certain margin than the intake stroke of the target cylinder.
Since the switching signal is output, the cam switching is reliably completed during the intake stroke of the target cylinder. Therefore, in order to absorb the torque shock caused by the cam switching, the output is adjusted by adjusting the throttle opening, ignition timing, etc. Regarding the correction control of
By targeting the intake stroke of the target cylinder, it is possible to synchronize correctly, avoiding the problem of further increasing the already large torque step due to the discrepancy between the actual cam switching and output correction control, and improving drivability. can be achieved. In addition, the target cylinder setting is set to the shortest cylinder without delay from the crank angle position at which the cam switching timing was determined, so it is possible to respond to cam switching requests with good response, improve fuel efficiency and output performance. can also be fully satisfied.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of the present invention, Fig. 2 is a plan view showing an embodiment of the present invention, Fig. 3 is a sectional view taken along line X-X, Fig. 4 is a characteristic diagram showing cam lift characteristics, and Fig. 5 is a diagram showing a cam lift characteristic. A characteristic diagram showing the full open output characteristics when using each cam, Figure 6 is a configuration diagram of the control system,
FIG. 7 (aHb) is an explanatory diagram showing torque fluctuations during cam switching, FIG. 8 is a flowchart showing cam switching control executed by the control unit, FIG. 9 is a timing chart of cam switching signals, and FIG. FIG. 10 is an explanatory diagram showing the setting of the response delay period for cam switching. 21-23...Cam, 24...Intake/exhaust valve, 25.
...Main rocker arm, 28.29...Sub rocker arm, 51...Control unit, 52.
...Crank angle sensor, 53...Accelerator operation amount sensor, 58...Cam position sensor. 25-1 To the inner rocker 7- 28.29---Puff rocker 7-m Figure 3 21-23- Cam Figure 4 Figure 5 Ensemble 25-in-locker length rpm @10 Figure 7 (a)

Claims (1)

[Claims] 1. A low-speed output cam with characteristics that generate high output in the low rotation range, a high-speed output cam with characteristics that generate high output in the high rotation range, and a fuel efficiency set with characteristics that provide good fuel efficiency. A cam, a cam switching mechanism that selectively switches these cams depending on operating conditions and transmits the motion of the cam to at least one of an intake valve or an exhaust valve, and corrects and controls engine output in response to a cam switching signal. A variable valve system for an internal combustion engine, comprising: a means for detecting a crank angle of the engine; a means for detecting an operating state; a means for determining cam switching according to the operating state; means for calculating a crank angle position with a switching delay period added to the current crank angle position; means for determining a cylinder that is assumed to be in the intake stroke at this estimated crank angle position; When the stroke start point is before the approximate midpoint of the intake stroke start point of the next cylinder in the ignition order, the angle obtained by subtracting the expected angle from the approximate midpoint, and after the approximate midpoint. means for calculating, as a switching angle, an angle obtained by subtracting an expected angle from the approximate midpoint between the start point of the intake stroke of the next cylinder in the firing order and the start point of the intake stroke of the next cylinder; and a crank angle position. and means for outputting a cam switching signal to the cam switching mechanism when the calculated switching angle is reached.