JPH0338422Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a variable valve timing device that changes the opening and closing timing of intake and exhaust valves of an internal combustion engine.

[Conventional technology and problems]

The variable valve timing device was developed in 1986.
This is already known as disclosed in Japanese Patent No. 27693, and the valve lift amount and valve timing are changed depending on the engine load. However, when the engine is operated with the throttle valve fully open, the valve timing required for the engine to produce maximum output varies depending on the engine speed. The volumetric efficiency of intake air when the throttle valve is fully open is
To explain using Figures a and b, when the intake valve is opened and closed as shown by the broken line l ₁ and the exhaust valve is opened and closed as shown by the broken line l ₂ , the volumetric efficiency of the intake air is ₃ , and on the other hand, when the intake valve is opened and closed as shown by the solid line m ₁ and the exhaust valve is opened and closed as shown by the solid line m ₂ , the volumetric efficiency of the intake air changes as shown by the solid line with respect to the engine speed.
It changes as shown by m ₃ . In other words, as can be understood from this figure, when the throttle valve is fully open,
It is possible to adjust the opening timing of the intake and exhaust valves depending on the engine rotation speed, but how the volumetric efficiency changes with respect to the engine rotation speed (Figure 8b)
may change slightly due to aging of intake and exhaust valves, etc.
Therefore, even if the opening/closing timing of the intake and exhaust valves is adjusted according to the engine speed, the optimum volumetric efficiency may not necessarily be obtained.

[Means for solving problems]

In view of the above points, the present invention provides a variable valve timing device that can obtain the optimum valve timing, especially when the throttle valve is fully opened. 1, an opening detection means 2 for detecting whether the opening of a throttle valve provided in the intake passage is equal to or higher than a predetermined value, and cylinder pressure near the intake bottom dead center and ignition timing during the compression stroke. means 3 for detecting the differential pressure between the cylinder pressure and the cylinder pressure at a previous predetermined crank angle position; and means 3 for detecting the operating timing of the drive mechanism so that the differential pressure is maximized when the opening degree of the throttle valve is greater than or equal to a predetermined value. It is characterized by comprising a control means 4 for adjusting.

〔Example〕

The present invention will be explained below with reference to the illustrated embodiments.

FIG. 2 shows an engine having a variable valve timing device according to an embodiment of the present invention. A piston 12 is slidably housed in a cylinder bore 11 formed in the engine body 10.
A combustion chamber 13 is formed by the cylinder bore 11 and the cylinder bore 11 . A mixture of air and fuel is introduced into the combustion chamber 13 through an intake port 14, and exhaust gas is exhausted to the outside through an exhaust port 15. The throttle valve 16 is provided in the intake passage 17 to adjust the amount of intake air, and the throttle opening switch 18 closes a contact when the opening of the throttle valve 16 is a predetermined value or more (for example, fully open) and sends an ON signal to the control device 40. It is designed to output to.

The intake port 14 and the exhaust port 15 are opened and closed by an intake valve 19 and an exhaust valve 20, respectively. The intake and exhaust valves 19 and 20 are driven to open and close by a cam 21 that presses these valve stems. A reference position sensor 23 is provided at the end of the cam shaft 22 on which the cam 21 is formed.
3 outputs a reference angle signal to the control device 40 when the cylinder in which it is installed is at the intake bottom dead center. For example, when there is one cylinder to measure the cylinder pressure, the reference position sensor 23 outputs a reference angle signal at the intake bottom dead center of that cylinder, and when there are multiple cylinders to measure the cylinder pressure, the reference position sensor 23 outputs a reference angle signal when any of those cylinders is at intake bottom dead center (see Figure 5b).

On the other hand, the crankshaft 24 provided below the piston 12 rotates in conjunction with the movement as the piston 12 moves up and down, and the angle sensor 25 provided at the end of the crankshaft 24 detects that the crankshaft 24 is at a predetermined angle ( For example, an angle signal is outputted to the control device 40 every time it rotates by 30 degrees (see FIG. 6c).

Further, the combustion pressure sensor 26 is arranged so as to face the combustion chamber 13, and detects the cylinder internal pressure, that is, the combustion pressure. A pressure signal output by the combustion pressure sensor 26 is input to the control device 40.

The control device 40 is composed of a microcomputer, and includes a central processing unit (CPU) 41, a read-only memory (ROM) 42, a random access memory (RAM) 43, an AD converter 44, an input interface circuit 45, and an output interface. circuit 46, these are bus lines 47
are interconnected by The ON signal of the throttle opening switch 18, the reference angle signal, and the angle signal are input to the input interface circuit 45,
The pressure signal is input to the AD converter 44 and AD converted. The program stored in ROM42 is
As will be described later, the opening and closing timings of the intake and exhaust valves 19 and 20 are determined based on these signals, and a control signal for changing the opening and closing timings is outputted via the output interface circuit 46. This control signal is input to the hydraulic unit 29, and the hydraulic unit 29 controls the opening and closing operations of the intake and exhaust valves 19 and 20 in accordance with the control signal, as described below.

Figure 3 shows the opening/closing timing adjustment mechanism. camshaft 22
is supported by a bearing 30 so as to be rotatable about the axis and also to be displaceable along the axis. An opening/closing gear 39 connected to a drive source is provided at the left end of the camshaft 22, a flange 31 is attached to the right end, and a spring 32 is provided between the flange 31 and the bearing 30 on the right side. The flange 31 is slidably housed within the cylindrical casing 33 to form a hydraulic chamber 34 . The pressure in the hydraulic chamber 34 is controlled by a hydraulic unit 29.
When the pressure in the hydraulic chamber 34 increases, the camshaft 22 is displaced to the left against the spring 32, and when the pressure in the hydraulic chamber 34 is released, the camshaft 22 is displaced to the right by the spring 32.
The cam 21 is thus displaced in the axial direction of the camshaft 22, thereby changing the contact position between the cam 21 and the valve lifter 35 provided at the end of the valve stem. The cam 21 has a nose portion 21 as shown in FIG.
The position a has a torsional positional relationship with respect to the axis of the camshaft 22, and therefore, when the axial position of the cam 21 changes, the opening and closing operations of the intake and exhaust valves 19 and 20 change.

The hydraulic unit 29 has a hydraulic controller 36, an oil pump 37, and an oil tank 38.
The hydraulic controller 36 is controlled by the control device 40 to supply the pressure oil fed from the oil pump 37 to the hydraulic chamber 34, or to return the pressure oil to the oil tank 38 to reduce the pressure inside the hydraulic chamber 34.

In this embodiment, the opening and closing timings of the intake and exhaust valves 19 and 20 are determined based on the cylinder internal pressure, and the reason for this will be explained next.

It can be seen from equation (51) below that the pressure P ₀ (absolute pressure) at the intake bottom dead center has a comparative relationship with the intake air amount.

P ₀ V ₀ =GRT ₀ (51) However, V ₀ takes a constant value at the stroke volume at intake bottom dead center, and R is a gas constant, which takes a constant value when the throttle valve 16 is substantially fully open. Therefore, the intake air weight G is G∝P ₀ /T ₀ (52) Furthermore, in this embodiment, changes in the intake air weight G are continuously detected under the same environment, and the temperature
Changes in T ₀ are negligible. Therefore, it can be expressed as G∝P ₀ (53). That is, in order to know the intake air weight G, it is sufficient to detect the pressure P ₀ at the intake bottom dead center, but since the amount of change in this pressure P ₀ is minute, it is difficult to detect this accurately. Therefore, in this embodiment, as described below, the pressure P ₁ before combustion and the pressure P ₀ at the intake bottom dead center are
The amount of change in the intake air weight G, that is, the amount of change in volumetric efficiency, is detected from the differential pressure ΔP.

Since there is an adiabatic change before combustion during the compression stroke, P ₀ V ₀ ^k = P ₁ V ₁ ^k (54) Here, as shown in Figure 5a, take the crank angle position C before combustion and calculate this _{When the cylinder pressure at the time} ^of _{​ ​} The closer the position C is to the top dead center, the larger the value of {(V ₀ /V ₁ ) ^k −1} becomes. That is, the closer the crank angular position C when detecting the pressure P ₁ is to the top dead center, the greater the differential pressure (P ₁ −P ₀ ) becomes, and the pressure P ₀ is amplified and detected. This crank angle position C needs to be set before combustion and is determined experimentally, for example, 40° BTDC.

Therefore, from equations (53) and (55) above, G∝P ₁ −P ₀ ...(56), that is, the change in the differential pressure between the pressure P ₀ at the intake bottom dead center and the pressure P ₁ at a predetermined crank angle position. It can be seen that by detecting , it is possible to detect a change in the amount of intake air, that is, the volumetric efficiency.

Therefore, in this embodiment, the control device 40
detects the difference in cylinder pressure between the intake bottom dead center and a predetermined crank angle position, and moves the camshaft 22 to adjust the opening/closing timing of the intake and exhaust valves 19 and 20 so that this differential pressure is maximized. . Figure 5a,
b and c indicate the change in cylinder pressure and the input timing of the reference angle signal and angle signal. As can be understood from this figure, the reference angle signal becomes ON when the piston reaches the intake bottom dead center, and the angle signal is transmitted at predetermined angle intervals (for example, 30 degrees CA) from when the reference angle signal becomes ON. becomes ON state. Further, the cylinder pressure is detected at a predetermined angle (for example, 40° BTDC) from the intake bottom dead center where the reference angle signal is output, as shown by arrows P and Q.
That is, the control device 40 has a counter in the RAM 43 that becomes 0 with the reference angle signal and is incremented by 1 every time the angle signal is input, and learns the crank angle position from the value of this counter and determines the intake bottom dead center. At the predetermined angle, the pressure signal output from the pressure sensor 26 is read and the differential pressure (P ₁ -P ₀ ) is detected. The control device 40 then calculates the amount of change in the opening/closing timing of the intake and exhaust valves based on this differential pressure in the direction of arrow R.

FIG. 6 shows a timing chart for controlling the opening and closing timing of the intake and exhaust valves 19 and 20.

The control device 40 sets the opening/closing timing of the intake and exhaust valves 19 and 20 to a constant value when the opening degree of the throttle valve 16 is small, and when the opening degree of the throttle valve 16 becomes large and the throttle opening switch 18 is turned ON. , and controls the opening/closing timing by displacing the camshaft 22. That is, when the throttle opening switch 18 is turned ON, the differential pressure in the cylinder is detected, and
The oil pressure flag is set to 1, the control oil pressure in the oil pressure chamber 34 begins to increase, and the camshaft 22 is displaced to the left in FIG. 3. At this time, the magnitude of the control hydraulic pressure is controlled by duty-controlling the opening time of a relief valve (not shown) in the hydraulic unit 29, and as the duty ratio decreases, the relief control amount decreases and the control hydraulic pressure increases. It's getting higher.
The operation of displacing the camshaft 22 based on the differential pressure in this way is executed every time the intake stroke is performed.

However, if the differential pressure in the next intake stroke is larger than the previous value, this means that the differential pressure has not yet reached its maximum value, and therefore it is necessary to further displace the camshaft 22. Therefore, the oil pressure control flag is held at 1, the relief control amount is decreased, and the control oil pressure is increased. If the camshaft 22 is moved even after the differential pressure continues to rise and reaches the maximum value in this way, the differential pressure decreases. Then, the oil pressure control flag is set to 0, the relief control amount increases, the control oil pressure decreases, and the camshaft 22 is displaced in the opposite direction (to the right in FIG. 3). As a result, the differential pressure increases again, so the relief control amount is decreased again, the control oil pressure is increased, and the camshaft 2
2 to the left in Figure 3. In this way, the differential pressure is maintained at approximately the maximum value, and the amount of intake air is maximized.

FIG. 7 shows a flowchart of a control program executed by the control device 40, and this program is interrupted every angle signal (for example, 30° crank angle).

In step 101, the throttle opening switch 1
8 is ON or not, and if it is not ON, the throttle valve 16 is not fully open, so steps 102,
103 is executed. That is, step 102
Then the control flag is set to 1, and then step 1
In step 03, an initial value is set as the relief control amount. Here, the initial value of the relief control amount is a duty ratio of 50% as shown in FIG. Then, in step 114, the step control amount is stored in the output register, and a command signal is output to the hydraulic unit 29 via this output register. Therefore, the control oil pressure in the hydraulic chamber 34 takes a value intermediate between the maximum value and the minimum value, so that the camshaft 22 takes a position intermediate between the left end position and the right end position.

If it is determined in step 101 that the throttle opening switch 18 is ON, the process proceeds to step 1.
04 and subsequent steps are executed, and the position of the camshaft 22 is controlled based on the differential pressure in the cylinder.

In step 104, it is determined whether or not the piston position is at the intake bottom dead center. If the piston position is at the intake bottom dead center, step 1
05, the detected value of the pressure sensor 26 at that time, that is, the A/D converted value of the cylinder internal pressure is continued. This value is stored in the RAM 43 as P ₀ . This ends the program, and when the next angle signal is output, the program is started again and steps 101 and 104 are executed in this order.
At step 104, since the piston is no longer at the intake bottom dead center, the process moves to step 106.
In step 106, it is determined whether the piston position is at a set angle (for example, 40° BTDC), but since it is not yet at the set angle at the beginning, the program ends.

After that, this program is executed several times, and when it is determined in step 106 that the piston position is at the set angle, the process moves to step 107, where the A/D converted value of the cylinder internal pressure at that time is continued, and this value is stored in the RAM ₄₃ as P1. In step 108, the difference between the pressure P ₁ and the pressure P ₀ is determined, and this differential pressure is stored in the RAM 43 as ΔP. It is determined in step 109 whether the differential pressure ΔP is greater than or equal to the previous differential pressure _{P_OLd} . When this step 109 is executed for the first time, _{P_OLd} is set to 0, and the process then proceeds to step 110.

In step 110, it is determined whether the control flag is 1 or not, but since it has already been set to 1 in step 102, the control flag is initially set in steps 111 and 112.
Move to. That is, in step 111, the relief control amount is subtracted by a predetermined amount, and processing is performed to increase the control oil pressure and displace the camshaft 22 to the left in FIG. 3. Next step 11
2, control flag 1 is set, and step 1
At step 13, the value of the differential pressure ΔP is set to P _OLd .
In step 114, the relief control amount determined in step 111 is stored in the output register. The hydraulic unit 29 is connected via this output register.
A command signal is output to the camshaft 22, thereby increasing the control oil pressure and displacing the camshaft 22. Therefore, the timing of opening and closing of the intake and exhaust valves 19 and 20 changes, and the differential pressure ΔP changes.

After the opening and closing timings of the intake and exhaust valves 19 and 20 are changed in this way, this program is executed to find the differential pressure ΔP again, and when step 109 is executed, this differential pressure ΔP is compared to the previous differential pressure. It is determined whether or not the value is greater than or equal to P _OLd . If the new differential pressure ΔP is larger than the original differential pressure P _OLd , that is, if the differential pressure ΔP still increases even after changing the opening/closing timing of the intake and exhaust valves, this means that the differential pressure ΔP has not yet reached its maximum value. means no,
Furthermore, processing is performed to move the camshaft 22 to the left. That is, steps 110, 11
1, 112, 113, and 114 are executed in this order, and the camshaft 22 is moved to the left.

However, when the differential pressure ΔP becomes smaller than the previous differential pressure _POLd in step 109, the process proceeds to step 11.
The process moves to step 5, where it is determined whether the control flag is 1 or not. If the control flag is 1 here, step 11
6, the relief control amount is added by the set amount, and at the same time, in step 117, the control flag 0 is set. Next steps 113, 11
4 is executed, and the camshaft 22 is moved to the right.

Similarly, in step 110, if the control flag is 1, the process moves to step 111, and the flag is set to 0.
If so, the process moves to step 116. Also step 1
At step 15, if the control flag is 1, the process moves to step 116, and if it is 0, the process moves to step 111. Due to this action, the differential pressure ΔP is maintained at its maximum value, and the volumetric efficiency of intake air is maximized.

Note that the above control does not necessarily apply to the throttle valve 16.
It is not necessary to perform this operation when the opening is completely open, but it may be performed when the opening is above a certain degree.

[Effect of idea]

As described above, according to the present invention, the volumetric efficiency of intake air can be maximized when the throttle valve is almost fully open, and the volumetric efficiency can always be maximized regardless of manufacturing errors or aging of each engine component. The effect is that it can be done.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of the present invention, Fig. 2 is a partial sectional view showing an engine to which one embodiment is applied, Fig. 3 is a partial sectional view showing the opening/closing timing adjustment mechanism, and Fig. 4 is a perspective view showing the cam. , Fig. 5 a is a graph showing the temporal change of the pressure signal, Fig. 5 b is a graph showing the reference angle signal, Fig. 5 c is a graph showing the angle signal, and Fig. 6 shows the throttle opening switch in ON state. 7 is a flowchart of the control program by the control device, and FIG. 8a is a graph showing changes in valve lift amount with respect to crank angle.
FIG. 8b is a graph showing changes in volumetric efficiency with respect to engine rotational speed. 16...throttle valve, 18...throttle opening switch, 19...intake valve, 20...exhaust valve,
21...Cam, 26...Pressure sensor, 29...Hydraulic unit, 40...Control device.

Claims (1)

[Scope of utility model registration request] A drive mechanism that opens and closes the intake and exhaust valves, an opening detection means that detects whether the opening of the throttle valve provided in the intake passage is above a predetermined value, and a cylinder pressure and compression near the intake bottom dead center. means for detecting the differential pressure between the cylinder pressure at a predetermined crank angle position during the stroke and before the ignition timing; and a control means for adjusting the operating timing of the drive mechanism.