JP3663788B2 - Valve timing control device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a valve timing control device that changes a valve timing of an engine in accordance with an operating state of an internal combustion engine and controls a valve overlap amount between an intake valve and an exhaust valve of the engine.
[0002]
[Prior art]
Conventionally, there has been known a valve timing control device that changes the opening / closing timing (valve timing) of an intake / exhaust valve in accordance with the operating state such as the rotation speed and load of an internal combustion engine and improves output and fuel consumption in each operating state. Yes.
In this type of valve timing control device, a period in which both the intake valve and the exhaust valve are simultaneously opened by changing the valve timing (hereinafter, the length of this period is referred to as “valve overlap amount”). Is set to an optimal value to improve engine performance in each operating state.
[0003]
An example of this type of valve timing control device is disclosed in, for example, Japanese Patent Laid-Open No. 4-194331.
The device in the publication switches the valve timing according to the engine operating state, sets a small valve overlap amount during low-speed and low-load operation, and further overlaps the valve in the entire operation region during cold operation when the engine temperature is low. The amount is set small.
[0004]
In general, when the valve overlap amount is set to be large, the period during which the intake valve is opened together with the exhaust valve during the exhaust stroke becomes longer, and so-called burned gas blows back, in which the burned gas in the cylinder flows backward to the intake port. It becomes easy. In particular, when the engine is under low load operation, the throttle valve opening is small and the intake port negative pressure is large (that is, the absolute pressure in the intake port is low). Become.
[0005]
When the amount of burnt gas blown back to the intake port is large, the amount of fresh air supplied to the cylinder decreases due to the reburned gas that has flowed back to the intake port being re-intaked into the cylinder during the intake stroke. (Increase of internal EGR amount) occurs, and particularly when the engine temperature is low, the amount of fuel (wall surface attached fuel) adhering to the intake port wall surface increases among the fuel supplied to the intake port. There is a problem that fuel is not supplied to the cylinder.
[0006]
That is, when the engine temperature is low, the fuel supplied to the intake port is difficult to evaporate, so that relatively large liquid fuel particles are formed in the intake port. If the burnt gas flows backward to the intake port in this state, the fuel particles in the intake port are blown back and adhere to the wall surface. Further, the lower the engine temperature, that is, the worse the fuel vaporization state, the greater the amount of fuel adhering to the wall surface. For this reason, when burnt gas blows back at low temperatures, the fuel wall adheres to the cylinder, so that sufficient fuel is not supplied to the cylinder, causing cold hesitation (so-called “shaking during low-temperature acceleration”) or an increase in the amount of internal EGR. There is a problem that combustion becomes unstable.
[0007]
In the above Japanese Laid-Open Patent Publication No. 4-194331, during low-rotation and low-load operation where the intake port negative pressure is large and blowback is likely to occur, the valve overlap amount is reduced to reduce burnt gas blowback, and the internal EGR amount is increased. In addition to preventing deterioration of combustion, the valve overlap amount is reduced in the entire operation region during cold operation where the engine temperature is low, thereby reducing the amount of fuel adhering to the wall surface due to blown back of burned gas.
[0008]
As described above, in the apparatus of the above publication, in order to stabilize combustion by reducing the amount of internal EGR at low temperatures and to prevent cold hesitation by reducing wall-attached fuel at low temperatures, the valve is lower than at high temperatures at low engine temperatures. The overlap amount is set small.
In addition to the above, there is a problem that the operating speed of the variable valve timing mechanism that changes the valve timing is reduced when the engine temperature is low, and misfire of the engine is likely to occur depending on changes in operating conditions. That is, at low temperatures, the operating speed of the variable valve timing mechanism becomes slow due to an increase in friction at each part and an increase in the viscosity of the hydraulic oil. For this reason, it takes a long time to change the valve overlap amount to a size suitable for the operating conditions when the engine temperature is low. There is a temporary difference between the optimum valve overlap amount and the actual valve overlap amount. In this case, when the valve overlap amount is smaller than the optimum value, there is a problem that the engine output is reduced, but no major problem occurs in the operation of the engine. However, if the valve overlap is excessively large with respect to the optimum value, a misfire may occur, and in an extreme case, the engine may not be operated. For this reason, the valve overlap amount is usually set smaller than that at high temperature when the engine is cold, and even if the operating speed of the variable valve timing mechanism decreases, the actual valve overlap amount may become excessively larger than the optimum value. In order to prevent this, misfires are prevented at low temperatures.
[0009]
In other words, conventionally, for the purpose of (1) reduction of internal EGR, (2) reduction of fuel adhering to the wall, and (3) prevention of misfire due to delay of the operation speed of the variable valve timing mechanism, the valve overlap amount is reduced at the engine low temperature. Setting was made smaller than at high temperatures.
[0010]
[Problems to be solved by the invention]
However, if the valve timing control device that changes the valve overlap amount of the cylinder by changing the valve timing is controlled to uniformly reduce the valve overlap when the engine temperature is low, as in the device described in the above publication, the engine performance at low temperatures There is a problem of greatly decreasing. When changing the valve overlap amount by changing the valve timing, the valve opening period of the normal valve is kept constant. In other words, considering the case where the valve overlap is controlled by changing the opening / closing timing of the intake valve, as the opening / closing timing of the intake valve is advanced (advanced), the valve overlap amount increases and becomes slower ( The more you retard, the less valve overlap. For this reason, when changing the valve overlap amount by controlling the valve timing, if the valve overlap amount is set to a small value, the closing timing of the intake valve will be delayed at the same time, and the intake valve will be compressed after the end of the intake stroke of the cylinder. It will come to close inside. As described above, when the closing timing of the intake valve is applied to the compression stroke, the intake air once sucked into the cylinder is pushed back from the intake valve to the intake port during the compression stroke, and the intake volume efficiency of the cylinder is reduced. Problems arise. In particular, when the engine is running at a low speed, the supercharging effect due to the intake inertia can hardly be obtained. Therefore, if the closing timing of the intake valve is delayed, the reduction in the engine output due to the reduction in the intake volume efficiency also increases.
[0011]
On the other hand, for example, when fuel on the wall surface is considered, even when the engine is at a low temperature, if the fuel vaporization state is good, the fuel wall surface hardly adheres even if the burned gas blows back slightly due to valve overlap. For this reason, even when the engine temperature is low, the amount of valve overlap can be increased when light fuel with good vaporization is used, compared to when heavy fuel with poor vaporization is used. It should be possible.
[0012]
Also, if the variable valve timing mechanism has low friction, or if the operating speed of the variable valve timing mechanism is high even at low temperatures, such as when low-viscosity oil is used, the operating speed is low. In contrast, even if the valve overlap at a low temperature is set large, misfire or the like should not occur.
For this reason, if the valve overlap amount is uniformly set to be small when the engine temperature is low as in the device disclosed in Japanese Patent Laid-Open No. 4-194331, the valve overlap is not necessary depending on the operating conditions. There is a case where the operation is performed by setting the amount small and reducing the engine output.
[0013]
In view of the above problems, the present invention minimizes the reduction of the valve overlap amount even when the engine temperature is low, and reduces the conventional engine output when adjusting the valve overlap amount by changing the valve timing. An object of the present invention is to provide a valve timing control device capable of improving the engine output under the generated conditions.
[0014]
[Means for Solving the Problems]
  According to the invention described in claim 1,Valve timing control that adjusts the valve overlap amount of the engine according to the operating state of the internal combustion engine by changing the valve timing of the internal combustion engine and sets the valve overlap amount of the engine to be smaller than that at the high temperature of the engine at a low temperature of the engine In the apparatus, the operating speed detecting means for detecting the valve timing change speed when the valve timing is changed, and the valve overlap amount when the engine temperature is low are larger when the valve timing change speed is larger than when the valve timing change speed is small. There is provided a valve timing control device for an internal combustion engine, which includes an operation speed correction means for correcting the operation speed.
[0015]
  According to invention of Claim 2,Furthermore, a rotation speed detection means for detecting the engine rotation speed is provided, and a rotation speed correction means for correcting the valve overlap amount when the engine temperature is low to be larger when the engine rotation speed is high than when the engine rotation speed is low. A valve timing control device according to claim 1 is provided.
[0016]
  According to invention of Claim 3,Further, a fuel determination means for determining the property of the fuel used in the engine, and when the fuel determination means determines that the engine fuel is a light fuel, the engine valve fuel is heavy when the engine fuel is a light fuel. A valve timing control device according to claim 1, further comprising: a fuel correction unit that corrects the fuel to be larger than when determined to be fuel.
  According to the invention of claim 4, the fuel determination means determines the property of the fuel used in the engine based on the change in the fuel temperature in the fuel tank and the change in the fuel tank pressure after the engine is started. A valve timing control device according to claim 3 is provided.
[0017]
  In the invention of claim 1,When the engine is cold, the valve overlap amount is set to a smaller value than when the engine is hot. However, if the valve timing change speed (the operating speed of the variable valve timing mechanism) is fast, the valve timing changes even at low temperatures. The valve overlap amount is corrected to a larger value than when the speed is low. Therefore, even when the engine is cold, the variable valve timing mechanism has a fast response speed, and the valve overlap amount is large when the difference between the optimal valve overlap amount and the actual valve overlap amount does not increase. Set to
[0018]
  Furthermore, in the invention of claim 2,In Claim 1, the valve overlap amount is corrected in accordance with the engine speed. That is, since the discharge pressure and the discharge flow rate of the variable valve timing mechanism hydraulic pump increase at a high engine speed, the operating speed of the variable valve timing mechanism becomes faster than that at the low engine speed. Therefore, if the valve overlap is controlled based on the variable valve timing mechanism operating speed detected by the operating speed detecting means at a low engine speed, the valve overlap amount at a high engine speed may not necessarily be appropriate. In the second aspect of the invention, the rotational speed correction means corrects the valve overlap amount corrected by the operating speed correction means in accordance with the engine rotational speed. Thereby, the change by the engine speed of the variable valve timing mechanism operating speed is corrected.
[0019]
  In the invention of claim 3,In claim 1, when the engine operating fuel is light fuel, the valve overlap amount is corrected so as to be larger than when the engine operating fuel is heavy fuel. Therefore, even when the engine is cold, the valve overlap amount is corrected according to the ease of vaporization of the fuel used. Set to a large value.
  According to the invention of claim 4, the fuel used in the engine is determined based on the change in the fuel temperature in the fuel tank and the change in the pressure in the fuel tank after the engine is started, whereby the fuel vaporization tendency is accurately determined. .
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration when the valve timing control device of the present invention is applied to an intake valve of a four-cycle engine.
In this embodiment, a double overhead camshaft (DOHC) type engine having separate camshafts is used for driving the intake valve and the exhaust valve, and the variable valve timing mechanism is provided only on the intake camshaft. Yes. In other words, in this embodiment, the valve timing of the exhaust valve is not changed, and only the valve timing of the intake valve is changed according to the operating conditions to change the valve overlap between the intake valve and the exhaust valve. The present invention is not limited to this embodiment, and the present invention can be applied to those that change the valve timing of only the exhaust valve or those that change the valve timing of both the intake valve and the exhaust valve.
[0021]
In FIG. 1, reference numeral 1 denotes an intake camshaft that opens and closes an intake valve (not shown) of a DOHC type engine, and reference numeral 10 denotes a variable valve timing mechanism provided at the end of the intake camshaft.
The variable valve timing mechanism 10 includes a timing pulley 12 having a cylindrical sleeve 13 and a cover 14 that covers the end of the camshaft 1. The timing pulley 12 is connected to the intake camshaft 1 via the cylindrical sleeve 13. The camshaft 1 is rotatably mounted around the camshaft 1. Further, the cover 14 is fixed to the timing pulley 12 by a bolt 15 so as to rotate integrally with the pulley 12.
[0022]
A piston member 17 is provided inside the cover 14. The piston member 17 includes an annular piston portion 19 and a cylindrical portion 21 extending from the piston portion 19, and the outer peripheral surface and inner peripheral surface of the piston portion 19 are the inner peripheral surface of the cover 14 and the pulley 12. Each is in sliding contact with the outer peripheral surface of the sleeve 13. Further, an outer helical gear 21a and an inner helical gear 21b having a predetermined twist angle are formed on the outer peripheral surface and the inner peripheral surface of the cylindrical portion 21 of the piston member 17, respectively. The internal helical gear 22a formed on the surface and the inner helical gear 21b mesh with the ring-shaped external helical gear 22b integrally attached to the end surface of the camshaft 1 by bolts 1a and pins 1b.
[0023]
In the variable valve timing mechanism 10 of the present embodiment, the rotation of the crankshaft (not shown) of the engine is transmitted to the timing pulley 12 via the timing belt 12a. When the pulley 12 rotates, the cover 14 rotates integrally with the pulley 12, and the piston member 17 connected to the cover 14 via the helical gears 22a and 21a rotates integrally with the cover 14. Since the piston member 17 is simultaneously connected to the camshaft 1 via the helical gears 21b and 22b, the camshaft 1 rotates integrally with the pulley 12.
[0024]
That is, in the variable valve timing mechanism 10 of this embodiment, the rotational driving force of the camshaft 1 is transmitted from the crankshaft to the timing pulley 12 via the timing belt 12a, and from the pulley 12 to the cover 14, the helical gears 22a and 21a, the piston It is transmitted to the camshaft 1 through the member 17 and the helical gears 21b and 22b.
[0025]
The variable valve timing mechanism 10 of the present embodiment changes the valve timing of the intake valve by moving the piston member 17 in the direction of the camshaft 1 axis.
That is, the piston member 17 is connected to the cover 14 and the camshaft 1 by helical gears 22a, 21a and 21b, 22b having respective predetermined twist angles that mesh with each other. Therefore, when the piston member 17 moves in the camshaft axial direction, the meshing positions of the helical gears 22a and 21a and 21b and 22b move in the axial direction along the respective tooth traces. However, since the tooth surface of each gear has a twist angle with respect to the axial direction of the camshaft, when the meshing position moves in the axial direction, the cover 14 and the piston member 17 and the piston member 17 and the camshaft 1 are respectively Relative movement in the circumferential direction along the helical gear teeth. For this reason, as the piston member 17 moves in the axial direction, the cover 14 and the piston member 17 and the piston member 17 and the camshaft 1 rotate relatively. Accordingly, by moving the piston member 17 in the camshaft 1 axial direction during operation of the engine, the rotational phase of the timing pulley 12, that is, the rotational phase of the camshaft 1 relative to the rotational phase of the crankshaft can be advanced (or delayed). Therefore, the opening / closing timing of the intake valve driven by the camshaft 1 can be advanced (or retarded).
[0026]
As described above, since the variable valve timing mechanism 10 of the present embodiment changes only the rotation phase of the intake camshaft 1, the valve opening timing and the valve closing timing of the intake valve are changed when the valve timing is changed. It always changes by the same amount, and the valve opening period of the intake valve itself is kept constant.
In the present embodiment, the valve timing change operation of the intake valve is performed by moving the piston member 17 using hydraulic pressure during engine operation. As shown in FIG. 1, two oil passages 2 and 3 are formed in the camshaft 1 along the axial direction. The oil passage 2 is provided at the center of the camshaft 1, and the shaft end side of the oil passage 2 is formed between the inner surface of the cover 14 and the shaft end side end surface of the piston member 17 through a port 2 a drilled in the bolt 1 a. The hydraulic chamber 5 communicates with the hydraulic chamber 5. The other end of the oil passage 2 is connected to a linear solenoid valve 25 (to be described later) via a port 2b formed in the camshaft 1 in the radial direction. On the other hand, the shaft end side end portion of the oil passage 3 is closed by the ring-shaped external gear 22b. The oil passage 3 communicates with a hydraulic chamber 8 formed by the end face of the piston member 17, the timing pulley 12 and the cover 14 via a port 3a formed in the radial direction, and via another port 3b. It communicates with the linear solenoid valve 25.
[0027]
The linear solenoid valve 25 is a spool valve having a spool 26, and is connected to the hydraulic port 26a connected to the port 2b of the oil passage 2 via a pipe and to the port 3b of the oil passage 3 via a pipe. A hydraulic port 26b, a port 26c connected to a hydraulic pressure supply source 28 such as an engine lubricating oil pump, and two drain ports 26d and 26e are provided. The spool 26 of the valve 25 operates to selectively connect one of the ports 26a and 26b to the port 26c and connect the other to the drain port.
[0028]
That is, when the spool 26 moves leftward in FIG. 1, the port 26a communicating with the port 2b of the oil passage 2 is connected to the hydraulic pressure supply source 28 via the port 26c, and the drain port 26d is closed. At the same time, the port 26b connected to the port 3b of the oil passage 3 communicates with the drain port 26e. Therefore, the lubricating oil flows into the hydraulic chamber 5 of the variable valve timing mechanism 10 from the hydraulic supply source 28 such as an engine lubricating oil pump through the oil passage 2 and the port 2a, and the piston member 17 is moved to the right in FIG. To push. At this time, the lubricating oil in the hydraulic chamber 8 is discharged from the drain port 26e from the port 3a through the oil passage 3, the port 3b, the port 26b of the linear solenoid valve 25, and the like. For this reason, the piston member 17 moves rightward in FIG.
[0029]
In contrast, when the spool 26 moves to the right in FIG. 1, the port 26b is connected to the port 26c, and the port 26a is connected to the drain port 26d. As a result, the lubricating oil flows into the hydraulic chamber 8 through the oil passage 3, and the lubricating oil is discharged from the hydraulic chamber 5 through the oil passage 2 to the drain port 26d. Move in the direction.
[0030]
In this embodiment, when the lubricating oil is supplied to the hydraulic chamber 5 and the piston member 17 moves rightward in FIG. 1, the intake valve timing is changed to the advance side, and the lubricating oil is supplied to the hydraulic chamber 8. The torsion angles of the helical gears 21a, 21b and 22a, 22b are set so that the intake valve timing is changed to the retard side when the piston member 17 moves to the left in FIG.
[0031]
Also, a linear solenoid actuator that drives the spool 26 is indicated by 25b in FIG. The linear solenoid actuator 25b receives a control signal from a control circuit 30 to be described later, and moves the spool 26 by an amount proportional to the magnitude of this control signal, thereby adjusting the position of the piston member 17, that is, the valve timing of the intake valve. change.
[0032]
1 is a control circuit for controlling the operation of the linear solenoid valve 25. In the present embodiment, the control circuit 30 connects a read only memory (ROM) 32, a random access memory (RAM) 33, a microprocessor (CPU) 34, an input port 35, and an output port 36 to each other via a bidirectional bus 31. A digital computer having a known configuration is configured. In addition, the control circuit 30 includes a backup RAM 37 that is directly connected to a power source such as a battery and can retain data even when the engine is stopped. The control circuit 30 of the present embodiment controls the operation of the linear solenoid valve 25 in accordance with the engine operating conditions, adjusts the valve timing of the intake valve, and controls the valve overlap amount of the intake and exhaust valves. For this control, the input port 35 of the control circuit 30 is provided with a voltage signal proportional to the engine intake air amount (volume flow rate) from the air flow meter 41 provided in the intake passage of the engine and the engine cooling water passage. A voltage signal proportional to the engine coolant temperature THW is input from the water temperature sensor 42 via the AD converter 43, and the crankshaft rotation angle CA provided from the crankshaft rotation angle sensor 44 provided on the engine crankshaft. And a pulse signal representing the rotation angle CMA of the camshaft 1 from a cam rotation angle sensor 45 provided on the camshaft.
[0033]
In this embodiment, a fuel tank (not shown) of the engine is provided with a fuel temperature sensor 47 for detecting the fuel temperature in the tank and a fuel tank pressure sensor 49 for detecting the fuel tank internal pressure. A voltage signal proportional to the fuel temperature FT from 47 and a voltage signal proportional to the tank internal pressure FP from the sensor 49 are respectively input to the input port 35 of the control circuit 30 via the AD converter 43.
[0034]
The engine intake air amount detected by the air flow meter 41 is converted into a weight flow rate G by a known method, and the intake weight flow rate GN (= G / NE) per one rotation of the engine is further changed at regular intervals using the engine speed NE. And stored in the RAM 33 of the control circuit 30.
The pulse signal from the crankshaft rotation angle sensor 44 is composed of an N1 signal indicating the reference position of the crankshaft generated every crankshaft rotation 720 degrees and an NE signal generated every 30 degrees crankshaft rotation. The sensor 45 generates a CN1 pulse signal indicating that the camshaft has reached the reference position every 360 degrees of camshaft rotation. The control circuit 30 calculates the engine speed NE from the pulse interval of the NE signal at regular intervals, and uses the engine speed NE to calculate the rotational phase of the camshaft 1 (the intake valve) from the time interval between the N1 signal and the CN1 signal. (Actual valve timing) VT. The calculation result is stored in the RAM 33. Further, the coolant temperature THW is AD-converted at regular time intervals and stored in the RAM 33 in the same manner. That is, the detection values such as GN, NE, VT, THW, FT, and FP stored in the RAM 33 are updated at regular intervals, and the latest value is always stored in the RAM 33.
[0035]
As will be described later, the engine speed NE and the engine intake air amount GN are used as parameters representing engine load conditions. The coolant temperature THW is used for correction based on the engine temperature of the valve timing described later. Further, the tank fuel temperature FT and the tank pressure FP are used for determining the properties of the engine fuel.
On the other hand, the output port 36 of the control circuit 30 is connected to the actuator 25b of the linear solenoid valve 25 via the drive circuit 48, and supplies a control signal to the actuator 25b.
[0036]
In the present embodiment, the control circuit 30, together with the fuel temperature sensor 47 and the fuel tank pressure sensor 49, fuel property determination means for determining the fuel property, and fuel correction for correcting the valve overlap amount according to the fuel property at the time of low engine temperature. Functions as a means.
Next, the valve timing setting of the intake valve of the present embodiment will be described with reference to FIG.
[0037]
FIG. 2 is a diagram schematically showing a general opening / closing timing of the intake valve and the exhaust valve. In FIG. 2, TDC indicates the top dead center of the piston stroke, BDC indicates the bottom dead center, IO and IC are the opening timing and closing timing of the intake valve, and EO and EC are the opening timing and closing timing of the exhaust valve, respectively. It represents the time. As shown in FIG. 2, the intake valve opens before the exhaust stroke top dead center (TDC) and closes after the intake stroke bottom dead center (BDC). The exhaust valve opens before the explosion stroke bottom dead center (BDC) and closes after the exhaust stroke top dead center (TDC). As shown in FIG. 2, in the exhaust stroke, since the valve timing is set so that the intake valve opens (IO) before the exhaust valve closes (EC), both the intake valve and the exhaust valve are opened. There is a period (period indicated by OL in FIG. 2). In the present embodiment, the length (angle) of the period OL is referred to as a valve overlap amount. In the present embodiment, the angle from the intake valve opening timing to the top dead center is defined as the valve timing value VT. As can be seen from FIG. 2, in the present embodiment, the valve closing timing of the exhaust valve is fixed, so the valve timing value VT and the valve overlap amount OL correspond one-to-one. That is, a large VT (the intake valve opening timing IO is early) means that the valve overlap amount OL is also increased accordingly, and the VT is small (the intake valve opening timing IO is late). This means that the valve overlap amount OL is also reduced accordingly.
[0038]
In general, the influence of the setting of the valve timing VT (valve overlap OL) of the intake valve on the engine performance is as follows.
(1) When the valve overlap amount OL is set large by increasing VT, the burnt gas blows back to the intake port at a low load when the intake pipe negative pressure increases (the intake port absolute pressure decreases). Further, since the burned gas blown back to the intake port is re-inhaled into the combustion chamber, the amount of residual burned gas in the combustion chamber increases, so-called internal EGR effect increases. On the other hand, as the load increases, the throttle valve opening increases and the intake negative pressure decreases. Therefore, when the load is high, even if the valve overlap amount OL is set large, the burned-back gas burns back.
[0039]
(2) If the valve overlap amount OL is set small by decreasing VT, the valve opening timing and the valve closing timing of the intake valve are delayed as compared with the case where the valve overlap amount OL is large (FIG. 2, IO ′, IC ′ indicates the opening timing and closing timing of the intake valve when the valve overlap amount is set small). In this case, the period during which the intake valve is open during the compression stroke (the period indicated by IB in FIG. 2) becomes longer, so that fresh air sucked into the cylinder is discharged from the cylinder at the initial stage of the compression stroke in the low / medium speed rotation region. The cylinder is pushed back to the intake port, and the charging efficiency of the cylinder is lowered. Therefore, when the valve overlap amount OL is set small, the actual compression ratio of the cylinder is lowered.
[0040]
On the other hand, in the high speed region, the intake air flow rate becomes faster, so that an intake inertia effect occurs. As the valve closing timing is delayed, the charging efficiency is improved and the actual compression ratio is increased. For this reason, in the high engine speed region, if the valve overlap amount OL is set small, the actual compression ratio of the cylinder increases.
In the present embodiment, in consideration of the influence of the valve timing value on the engine performance, the intake valve valve timing is set in each operation region of the engine as described below.
[0041]
FIG. 3 shows an example of a set value of the valve timing value VT at the time of operation in the standard state in the present embodiment, that is, at the time of operation after completion of warming up of the engine. Hereinafter, the valve timing set value in this standard state is referred to as a basic valve timing value (tVVT).
In the table of FIG. 3, the vertical axis represents the intake air weight GN (gram / rev) used as a parameter representing engine load, and the horizontal axis represents the engine speed NE (RPM). The value tVVT is expressed in terms of the crankshaft rotation angle (° CA).
[0042]
As shown in FIG. 3, the basic valve timing value tVVT is maximum in the medium-medium-rotation load operation region (NE≈2400 to 3200 RPM in FIG. 3, GN≈1.0 to 1.25 grams / revolution region). The value is taken (that is, the valve overlap amount OL is also maximized), and the value becomes smaller as the rotational speed or load is separated from the middle rotation load region, and the valve overlap amount OL is also reduced.
[0043]
That is, in the present embodiment, in a low load region (for example, GN <1.00), the basic valve timing value tVVT (that is, the valve overlap amount OL) is set smaller as the load is lower, and the burnt gas is blown back. Combustion is stabilized by reducing internal EGR. In the middle load region, the valve overlap amount OL (basic valve timing value tVVT) is low or high when the internal EGR amount is significantly increased to improve emissions and reduce pumping loss. Larger overall. However, even in the middle load region, if the valve overlap amount OL is set too large in the low speed region, combustion instability is likely to occur. In addition, if the valve overlap amount OL is set large in the high speed medium load region, intake inertia can be used. On the contrary, since the charging efficiency is lowered, the valve overlap amount OL is set to a relatively small value in the low speed region and the high speed region. For this reason, in this embodiment, the basic valve timing value tVVT is set so that the valve overlap amount OL is maximized in the medium-speed medium load region.
[0044]
In the high load region, the VT is generally set small because it is necessary to reduce the internal EGR and increase the output. In particular, in the high speed region, as the VT is reduced, the effect of improving the fresh air charging efficiency due to the intake air inertia is greater. Therefore, the VT is set smaller than that in the low and medium speed regions. For this reason, in the present embodiment, in the high load region (region of GN> 1.25), the valve overlap amount OL decreases as the load increases. Further, in the same load, the high speed region (NE <1600 RPM) than the low speed region (NE <1600 RPM). NE> 3200 RPM), the basic valve timing value tVVT is set so that the valve overlap amount OL becomes small.
[0045]
Next, correction of the basic valve timing value tVVT at the time of engine low temperature according to the present embodiment will be described.
As described above, the valve timing tVVT (valve overlap amount) shown in FIG. 3 is in the standard state after the engine is sufficiently warmed up. However, when the engine temperature is low, the fuel vaporization state is poor, so if the burned gas blows back into the intake port, the liquid fuel particles supplied to the intake port are blown back into the intake port due to the burnt gas blowing back. There is a problem of adhering to the wall surface. When the engine temperature is low, the intake port wall surface temperature is low, and the fuel attached to the intake port wall surface is difficult to vaporize.Therefore, when the fuel wall surface adhesion occurs at a low engine temperature, the amount of fuel actually supplied into the cylinder decreases. Problems such as a slow rise in engine speed during low-temperature operation (so-called cold hesitation) occur. Therefore, in the present embodiment, the basic valve timing value tVVT in FIG. 3 is corrected based on the engine coolant temperature THW so that the actual valve overlap amount decreases as the engine temperature (engine coolant temperature THW) decreases. Therefore, the occurrence of cold hesitation is prevented.
[0046]
FIG. 4 is a graph showing the relationship between the coolant temperature THW and the valve timing temperature correction amount tVTHW based on THW. As shown in FIG. 4, the value of the temperature correction amount tVTHW is the value after the warm-up is completed (the coolant temperature THW is a predetermined value THW).₁Above) is set to 0 and THW <THW₁Is set to a larger value as the cooling water temperature THW is lower, and the cooling water temperature THW is set to a predetermined value THW.₀A constant large value is set in the following areas. As will be described later, the control circuit 30 determines the value of the temperature correction amount tVTHW from FIG. 4 based on the coolant temperature TWH, and sets the basic valve timing value tVVT determined from the engine speed and the load to the temperature correction amount tVTHW. The actual valve timing control target value VVT of the variable valve timing mechanism 10 is calculated as VVT = tVVT−tVTHW (where VVT ≧ 0).
[0047]
As a result, the valve timing control target value VVT after temperature correction is set to be smaller by the correction amount tVTHW corresponding to the coolant temperature THW from the basic valve timing value tVVT in FIG.
However, when the temperature correction is performed so that the valve overlap amount is reduced in the entire load region at a low engine temperature as described above, the supercharging effect due to the intake inertia is obtained due to the delay in the closing timing of the intake valve as described above. In the low / medium speed operation region where the engine cannot be operated, there is a problem in that the engine output decreases greatly due to a decrease in the actual compression ratio of the engine.
[0048]
By the way, the correction of the valve overlap amount by the engine temperature is mainly intended to prevent the fuel from adhering to the port wall surface when the burned gas blows back to the intake port when the engine temperature is low. However, if the fuel particles supplied to the intake port are vaporized or sufficiently atomized even at a low temperature of the engine, even if the burned gas blows back to the intake port, the adhesion of the fuel to the wall surface is reduced. On the other hand, the vaporization tendency of the fuel varies greatly depending on the composition of the fuel, and the vaporization state of the fuel containing a lot of light components (light fuel) is good even at a low engine temperature. For this reason, even when the engine temperature is low, if light fuel with good vaporization is used, it is difficult for the fuel to adhere to the wall surface, and cold hesitation is possible even if the valve overlap amount is set somewhat large. Such a problem does not occur.
[0049]
That is, if the valve overlap amount was set to be uniformly small at low engine temperatures, the valve overlap amount should be set small even when using light fuel that can increase the engine output by setting the valve overlap amount larger. As a result, the engine output is unnecessarily reduced. Therefore, in the present embodiment, the valve timing set value after performing the temperature correction described above is further corrected according to the properties of the fuel used in the engine, and the valve overlap amount is increased as the fuel used is lighter. ing. As a result, the valve overlap amount is reduced only when it is really necessary at low engine temperatures, and unnecessary reduction in engine output is prevented.
[0050]
As described above, in order to correct the valve overlap amount when the engine temperature is low according to the properties of the fuel used, it is necessary to accurately determine the vaporization tendency of the fuel currently used in the engine. In this embodiment, the fuel property is determined by the following method by measuring the change in the fuel temperature in the fuel tank and the change in the pressure in the fuel tank after the engine is started.
[0051]
FIG. 5 is a diagram for explaining the relationship between the pressure in the fuel tank (fuel vapor pressure) and the fuel temperature in the tank. The horizontal axis in FIG. 5 indicates the fuel temperature, and the vertical axis indicates the tank internal pressure. In the figure, curve A is a fuel containing a light component (light fuel), and curve B is a heavy component. The case of containing fuel (heavy fuel) is shown respectively. The pressure in the fuel tank increases as the fuel vapor pressure increases as the fuel temperature increases. At this time, the vapor pressure of the light fuel (curve A) that is easily vaporized as shown in FIG. 5 is higher than that of the heavy fuel (curve B) that is difficult to vaporize even at the same temperature. Becomes bigger. Also, as shown in FIG. 5, the difference between the tank internal pressure for light fuel and the tank internal pressure for heavy fuel increases as the fuel temperature increases. That is, the increase in the tank internal pressure while the fuel temperature rises by a certain amount becomes larger as the fuel is lighter (easily vaporized). Therefore, in the present embodiment, the fuel vaporization tendency is determined by measuring the increase in pressure in the tank (FIG. 5, ΔFP) while the fuel temperature rises by a predetermined temperature range (FIG. 5, ΔF). .
[0052]
6 and 7 are flowcharts for explaining a determination routine for determining the fuel property. This routine is executed by the control circuit 30 at regular intervals.
In this routine, the fuel property is determined every time the engine is started.
When the routine starts in FIG. 6, it is determined in step 601 whether or not the engine start has been completed. If the engine start has not been completed (when a start operation is being performed), the flag XFUEL, The XDT values are set to the initial value 1, respectively. Whether or not the engine has been started is determined, for example, based on whether or not the engine speed has increased to a predetermined value or higher (for example, 400 RPM or higher). XFUEL is a flag for executing the determination of the engine fuel property only once every time the engine is started. The value of the flag XFUEL is set to 0 in step 633 (FIG. 7) after the determination of the fuel property is completed. The Further, the flag XDT is a flag for storing the fuel temperature FT0 at the start of measurement and the tank internal pressure FP0. The value of XDT is set to 0 in step 621 after storing FT0 and FP0.
[0053]
If the engine start has been completed in step 601, the process proceeds to step 607 to determine whether or not the value of the flag XFUEL is set to 1. When XFUEL ≠ 1 (that is, when the fuel property determination has already been completed), the routine is immediately terminated without executing step 609 and the subsequent steps.
In step 607, if XFUEL = 1, the process proceeds to step 609, where the fuel remaining amount FL in the fuel tank, the fuel tank internal pressure FP, and the fuel temperature FT are read, and based on these values in steps 611 to 615. Thus, it is determined whether or not a precondition for determining the fuel property is satisfied.
[0054]
Preconditions determined from step 611 to step 615 are: (1) the fuel amount FL in the tank is larger than the minimum value (AL), and (2) the fuel temperature FT in the tank is within a predetermined temperature range (B <FT <C), and (3) the tank internal pressure FP is within a predetermined pressure range (D <FP <E), and any one of the prerequisites (1) to (3) above is satisfied. If not, the routine ends immediately without making a fuel property determination.
[0055]
Here, the conditions (1) to (3) are required when determining the fuel properties. In the present embodiment, as will be described later, in this embodiment, the fuel properties are determined based on the increase in temperature and pressure in the fuel tank. This is because it is necessary to perform measurement within a stable range of pressure rise. In other words, the condition (1) is required because when the fuel remaining amount in the tank is not equal to or greater than the predetermined minimum value, the increase in the pressure in the tank is small and a measurement error is likely to occur. What is required is that measurement is performed in a range where the increase in pressure in the tank with respect to the temperature increase is somewhat large (see FIG. 5). The reason why the condition (3) is required is that the fuel tank is usually provided with a pressure control valve for controlling the tank internal pressure to be within a certain range, so that the pressure range in which the pressure control valve does not operate. This is because it is necessary to carry out measurement with this.
[0056]
When all the conditions from step 611 to step 615 are satisfied, in steps 617 to 621, the tank internal pressure FP and the fuel temperature FT at the time when the conditions are satisfied are stored as the pressure FP0 and the temperature FT0 at the start of measurement, respectively. Steps 617 and 621 are provided to execute step 619 only once.
[0057]
The routine then proceeds to step 623 of FIG.
In FIG. 7, step 623, it is determined whether or not the current fuel temperature FT has increased by a predetermined temperature width ΔF from the temperature FT0 at the start of measurement (step 619). If the increase width is smaller than ΔF, step 625 is performed. Exit the routine without doing the following: If the fuel temperature has increased by ΔF from the start of measurement, the fuel tank internal pressure increase width ΔFP (= FP−FP0) from the start of measurement is calculated in step 625. In step 627, the fuel property basic learning value tKFUEL is determined based on ΔFP calculated in step 625.
[0058]
FIG. 8 is a diagram illustrating the relationship between ΔFP and tKFUEL. As shown in FIG. 8, in this embodiment, the value of tKFUEL is set to a larger value as the value of ΔFP is larger. As described with reference to FIG. 5, the increase range (ΔFP) of the pressure in the tank with respect to the predetermined temperature increase range (ΔF) increases as the fuel volatility (evaporation tendency) increases, that is, as the fuel becomes lighter. Therefore, in this embodiment, the value of the fuel property basic learning value tKFUEL is set to a larger value as the fuel is lighter.
[0059]
Steps 629 and 631 are steps for correcting the value of the fuel property basic learning value tKFUEL obtained in step 627 in accordance with the remaining fuel amount in the tank.
When the remaining amount of fuel in the tank is small (that is, the volume of the space above the fuel oil level in the tank is large), the increase in pressure in the tank with respect to the increase in fuel temperature is small. Therefore, it is considered that the value of tKFUEL obtained in step 627 is smaller than the true value as the current fuel amount in the tank is smaller. Therefore, in the present embodiment, the remaining fuel amount correction coefficient tKFL is determined in accordance with the value of the remaining fuel amount FL read in Step 609 (Step 629), and the true fuel property learning value KFUEL is set to KFUEL = tKFUEL × tKFL. It is calculated as
[0060]
FIG. 9 is a diagram showing the relationship between the remaining fuel amount correction coefficient tKFL and the remaining fuel amount FL. As shown in FIG. 9, the value of tKFL is set to a larger value as the value of the remaining fuel amount FL is smaller.
As described above, after calculating the fuel property learning value KFUEL, in step 633, the calculated KFUEL value is stored in the backup RAM 37 of the control circuit 30, and in step 635, the value of the flag XFUEL is set to 0, and the routine is terminated. As described above, when the value of the flag XFUEL is set to 0, the fuel property determination (steps 609 to 633) is not executed thereafter.
[0061]
8 and 9 used for calculating the fuel property learning value KFUEL is determined in advance based on the actual fuel tank and the fuel property by experiments or the like and stored in the ROM 32 of the control circuit 30.
Next, the valve timing control of the present embodiment using the fuel property learning value KFUEL will be described. FIG. 10 is a flowchart showing a valve timing control routine of the present embodiment. In this routine, the valve timing is set according to the engine operating condition, and the valve timing set value is corrected based on the engine coolant temperature and the fuel property as described above. This routine is executed by the control circuit 30 at regular intervals.
[0062]
When the routine starts in FIG. 10, in step 1001, the intake weight flow rate GN per engine revolution and the engine speed NE are read. Next, at step 1003, the basic valve timing tVVT is read from the relationship shown in FIG. 3 using the values of GN and NE. The relationship of FIG. 3 is stored in advance in the ROM 32 of the control circuit 30 as a numerical map using GN and NE.
[0063]
After the basic valve timing tVVT is calculated, in step 1005, the current coolant temperature THW is read. In step 1007, the temperature correction amount tVTHW is determined from the coolant temperature THW using the relationship of FIG. Here, the relationship of FIG. 4 is also stored in advance in the ROM 32 of the control circuit 30 in the form of a numerical map using the value of THW.
[0064]
Next, at step 1009, the fuel property learning value KFUEL calculated by the routine of FIG. 6 is read from the backup RAM 37. In step 1011, the fuel property correction amount tVFUEL is determined based on the value of KFUEL. FIG. 11 is a graph showing the relationship between the fuel property learning value KFUEL and the fuel property correction amount tVFUEL. As shown in FIG. 11, in the present embodiment, the value of the fuel property correction amount tVFUEL is set to a smaller value as the learned value KFUEL is larger, that is, as the fuel is lighter.
[0065]
In step 1013, the basic valve timing tVVT is corrected using the temperature correction amount tVTHW and the fuel property correction amount tVFUEL obtained as described above, and the valve timing set value VVT is calculated as VVT = tVVT−tVTHW−tVFUEL. .
Next, in steps 1015 and 1017, if the valve timing set value VVT corrected in step 1011 is a negative value, VVT is reset to 0, so that the valve timing set value VVT is always VVT ≧ 0. Restrict to.
[0066]
In step 1019, the linear solenoid valve 25 is controlled so that the actual valve timing VT detected by the camshaft rotation angle sensor 45 matches the set value VVT, and the routine is terminated. This control is, for example, PDI (Proportional Differential Integration) control based on a deviation between VVT and VT.
By performing the above correction, if the other conditions are the same, the valve timing is set to a smaller value as the engine temperature is lower, and the valve overlap amount is smaller as the engine temperature is lower. The valve timing VT is also corrected by the properties of the fuel used. If the other conditions are the same, the lighter the fuel used, the higher the valve timing VT, and the larger the valve overlap amount. become. For this reason, even when the engine temperature is low, if the fuel used is light, the valve overlap will be set to a larger value than when heavy fuel is used. It is prevented from occurring.
[0067]
Next, another embodiment of the valve timing control of the present invention will be described.
In the above-described embodiment, by correcting the valve timing according to the fuel properties, the valve overlap amount is increased to increase the valve overlap amount when using light fuel that does not require a small valve overlap setting even at low engine temperatures. The output drop was prevented. In contrast, in the present embodiment, the valve overlap amount is corrected according to the operating speed of the variable valve timing mechanism 10 instead of the fuel property.
[0068]
As described above, generally, when the engine temperature is low, the variable valve timing mechanism operating speed decreases due to an increase in the viscosity of the variable valve timing mechanism hydraulic fluid, an increase in friction of each operating portion, and the like. For this reason, when the engine load state changes and the valve timing control target value (optimal valve timing value) decreases, it takes a relatively long time for the actual valve timing to reach the control target value. Temporarily, the actual valve timing continues to be larger than the optimum valve timing value.
[0069]
In this case, since the valve overlap amount is also larger than the optimum value, the engine misfire occurs when the actual valve overlap amount is much larger than the optimum value. Therefore, in general, even when the operating speed of the variable valve timing mechanism decreases at low engine temperatures, the valve overlap at low engine temperatures prevents the actual valve overlap from becoming excessively large compared to the optimum value. The lap amount is set to be extremely small. That is, the normal setting value of the valve overlap amount at a low temperature is set in consideration of the case where the operating speed of the variable valve timing mechanism is significantly reduced.
[0070]
However, actually, the operating speed of the variable valve timing mechanism does not decrease uniformly even when the engine temperature is low. For example, when a low operating oil viscosity is used, the operating speed of the variable valve timing mechanism does not decrease so much even at low engine temperatures. Further, since the clearance of each part of the mechanism varies within a tolerance, depending on the product, the clearance of each part is large, and the friction at low temperature is small, so that there is a case where the operation speed does not decrease so much even at low temperature. In such a case, even if the valve overlap amount at a low temperature is set to a relatively large value, there is no possibility of misfire. For this reason, if the valve overlap amount at the low temperature is set to a small value uniformly, the engine output is unnecessarily reduced when the operating speed at the low temperature does not decrease so much.
[0071]
Therefore, in the present embodiment, the operating speed of the variable valve timing mechanism 10 is actually detected during engine operation, and the set value of the valve timing is corrected according to the detected operating speed.
FIG. 12 is a flowchart showing a correction amount calculation routine for detecting the operation speed of the variable valve timing mechanism and calculating the valve timing operation speed correction amount tVVTR according to the operation speed. This routine is executed by the control circuit 30 at regular intervals (for example, about every 100 milliseconds).
[0072]
When the routine starts in FIG. 12, in step 1201, a current actual valve timing value VT and a valve timing set value (control target value) VVT calculated in a later-described valve timing control routine (FIG. 14) are read. In step 1203, the change amount ΔVT of the valve timing value VT from the previous routine execution is ΔVT = | VT−VT._i-1Is calculated as |. VT_i-1Is the valve timing value at the time of the previous routine execution. Since this routine is executed at regular time intervals, this change amount ΔVT represents the actual operating speed of the current variable valve timing mechanism. In step 1205, VT is prepared for the next routine execution._i-1Update the value of.
[0073]
Next, at step 1207, it is determined whether or not the deviation | VVT−VT | between the valve timing control target value VVT and the current valve timing value VT is greater than a predetermined value A. If | VVT−VT |> A. Only steps 1209 to 1215 for calculating the operation speed correction amount are executed. The reason why the operation speed correction amount is calculated only when the deviation | VVT−VT | is larger than the predetermined value A is that the deviation between the control target value VVT and the actual valve timing VT is large to some extent, and the variable valve timing mechanism 10 This is because the valve timing value change amount ΔVT measured in a state where the operating speed is sufficiently large is adopted as the operating speed. That is, in a state where the deviation between the control target value and the actual valve timing value is large to some extent, the operating speed of the variable valve timing mechanism is also increased, and the variation in the operating speed is reduced. Therefore, by calculating the operation speed correction amount based on the change amount ΔVT measured in this state, the operation speed correction with high reliability can be performed.
[0074]
If the deviation | VVT−VT | is larger than the predetermined value A in step 1207, then in step 1209, whether or not the control target value VVT is larger than the actual valve timing value VT, that is, the current variable valve timing mechanism is It is determined whether the timing is being advanced (valve timing is being increased) or retarded (valve timing is being reduced). If the angle is advanced (VVT> VT), the process proceeds to step 1211, and the valve timing change amount (change speed) ΔVT calculated in step 1203 is used to operate from the relationship shown by curve A in FIG. A speed correction coefficient tVVTR is determined. If the angle is retarded (VVT ≦ VT), the process proceeds to step 1213, and the operating speed correction coefficient tVVTR is similarly determined from the relationship shown by curve B in FIG. In step 1215, the operating speed correction coefficient tVVTR determined in step 1211 or step 1213 is stored as the actually used operating speed correction amount VVTR, and the routine is terminated.
[0075]
FIG. 13 is a diagram showing the relationship between the operating speed correction coefficient tVVTR and the variable valve timing mechanism operating speed ΔVT. Normally, the variable valve timing mechanism receives a reaction force from the cam shaft in either the advance side or the retard side. Then, the operating speed ΔVT is different. Therefore, in the present embodiment, during the advance operation (curve A) and during the retard operation (curve B), the same operation speed correction coefficient tVVTR can be obtained regardless of whether the advance operation or the retard operation is being performed. These curves are prepared and selected according to whether the measured ΔVT is in advance or retard. FIG. 13 shows the case where the variable valve timing mechanism receives a reaction force from the cam shaft in the valve timing retarding direction (when the operating speed of the retarding operation is faster than the operating speed of the advance operation).
[0076]
FIG. 14 is a flowchart of a valve timing control routine of the present embodiment that performs correction according to the operating speed of the variable valve timing mechanism using the operating speed correction amount VVTR. This routine is executed by the control circuit 30 at regular intervals.
In FIG. 14, when the routine is started, in steps 1401 to 1407, the basic valve timing tVVT based on GN and NE is set, and the temperature correction amount tVTHW is determined based on the engine temperature. Steps 1401 to 1407 are the same as steps 1001 to 1007 in FIG.
[0077]
When step 1407 ends, in this routine, the valve timing is corrected based on the variable valve timing mechanism operating speed in step 1409 and thereafter. That is, in step 1409, the operating speed correction amount VVTR calculated in the routine of FIG. 12 is read. In step 1411, the basic valve timing tVVT is corrected using the temperature correction amount tVTHW and the operating speed correction amount VVTR calculated in step 1407. Then, the valve timing set value VVT is set as VVT = tVVT−tVTHW + VVTR. That is, the valve timing is advanced as the operating speed correction amount VVTR increases, and the valve overlap increases. As described above, the operating speed correction amount VVTR is set to a larger value as the operating speed of the variable valve timing mechanism increases (FIG. 13). Therefore, in this embodiment, the valve overlap amount is variable even at low engine temperatures. The larger the timing mechanism operating speed, the larger the value is set.
[0078]
After the valve timing VVT is set as described above, in step 1413 to step 1419, the valve timing set value VVT is limited to a positive value and does not exceed the basic valve timing tVVT. In step 1421, based on the limited VVT. The variable valve timing mechanism 10 is controlled.
In the present embodiment, the variable valve timing mechanism operating speed is large even when the engine is cold due to the above routine execution, and the valve overlap amount does not need to be set small. Therefore, it is possible to prevent a reduction in engine output that is not necessary even when the engine temperature is low.
[0079]
Next, an embodiment different from FIG. 12 for calculating the correction amount VVTR based on the operating speed of the variable valve timing mechanism will be described. In the embodiment of FIG. 12, the correction amount VVTR is calculated based on the change rate ΔVT of the valve timing value when the difference between the valve timing set value VVT and the actual valve timing value VT is large. However, in practice, the operating speed of the variable valve timing mechanism varies with the engine speed. For example, when the engine is running at a low speed, the rotational speed of the engine-driven hydraulic pump is also reduced. For this reason, the hydraulic pressure of the variable valve timing mechanism hydraulic oil decreases, and the operating speed of the variable valve timing mechanism also decreases. Conversely, at the time of high engine speed, the rotational speed of the hydraulic pump increases and the hydraulic oil pressure increases, so that the variable valve timing mechanism operating speed increases.
[0080]
On the other hand, in the routine shown in FIG. 12, as described above, the operating speed correction amount VVTR is calculated only when the deviation between the set value VVT and the actual valve timing value VT is large. Become. Therefore, if the engine speed at the time of VVTR calculation and the engine speed at the time of correcting the valve timing using the VVTR are different, the actual variable valve timing mechanism operating speed and the correction amount VVTR will not correspond. There is a fear. That is, if the valve timing correction is performed at the time of high engine speed using the VVTR calculated at the time of low engine speed, the increase amount of the valve overlap will be set small even though the variable valve timing mechanism operating speed is actually high. (FIG. 14, step 1411). On the other hand, if the VVTR calculated at the time of high engine speed is used and the correction of step 1411 in FIG. 14 is performed at the time of low engine speed, the valve overrun will actually occur even though the operating speed of the variable valve timing mechanism has decreased. There is a risk that the lap will be set large.
[0081]
Therefore, in the present embodiment, the difference in the operating speed caused by the difference in the rotational speed is corrected by performing correction based on the engine speed at the time of calculating the operating speed correction amount VVTR and at the time of valve timing correction based on the VVTR. Yes.
FIG. 15 shows an example of a change in operating speed of the variable valve timing mechanism depending on the engine speed. FIG. 15A shows a change in the discharge pressure of the engine-driven hydraulic pump depending on the engine speed. As shown in FIG. 15A, the pump discharge pressure increases as the engine speed increases. FIG. 15 (B) shows the change in the operating speed of the variable valve timing mechanism due to the change in hydraulic pressure in FIG. 15 (A). As shown in FIG. 15 (B), the variable valve timing mechanism operating speed shows substantially the same change as the discharge pressure of the hydraulic pump.
[0082]
In the present embodiment, a rotational speed correction coefficient tVNE determined according to the rotational speed based on the characteristics shown in FIG. 15 is introduced to correct the operating speed correction amount VVTR. FIG. 16 shows the relationship between the rotational speed correction coefficient tVNE and the engine rotational speed NE. As shown in FIG. 16, the rotation speed correction coefficient tVNE is set to have the same characteristics as in FIG.
[0083]
FIG. 17 is a flowchart showing an operation speed correction amount VVTR calculation routine using the correction coefficient tVNE. 17, Steps 1701 to 1713 are steps for calculating the operating speed correction coefficient tVVTR from the valve timing value variation ΔVT, and are the same as Steps 1201 to 1213 of FIG. . In this embodiment, after calculating the operating speed correction coefficient tVVTR as described above, the current engine speed NE is read in Step 1715, and in Step 1717, this speed NE is used to calculate the speed correction coefficient tVNE from the relationship of FIG. Is calculated. In step 1719, a value obtained by dividing tVVTR by tVNE is a basic operation speed correction amount VVTR.₀Remember as.
[0084]
FIG. 18 shows the correction amount VVTR stored as described above.₀Is a flowchart showing a valve timing control routine of the present embodiment using the rotation speed correction coefficient tVNE. The routine of FIG. 18 differs only in that step 1810 and step 1810a are added between steps 1409 and 1411 of the routine of FIG. 14, and steps 1801 to 1809 are different from steps 1401 to 1409 of FIG. Steps 1811 to 1821 are the same as steps 1411 to 1421 in FIG.
[0085]
In FIG. 18, in step 1809, the basic operating speed correction amount VVTR set in FIG.₀In step 1810, a speed correction coefficient tVNE corresponding to the current engine speed NE is calculated based on FIG. Then, using the engine speed correction coefficient tVNE based on the current engine speed, the basic correction amount VVTR₀Correct the value of again. That is, VVTR₀The value obtained by multiplying the value by the correction coefficient tVNE is used as the operating speed correction amount VVTR, and the valve timing correction in step 1811 and subsequent steps is performed.
[0086]
Thus, the correction amount VVTR₀By making corrections using the engine speed at the time of calculation and at the time of valve timing correction, it is possible to accurately make corrections based on the variable valve timing mechanism operating speed regardless of changes in engine speed. It becomes. For example, the value of tVVTR (steps 1711 and 1713 in FIG. 17) calculated at the time of high engine speed is obtained by dividing the value obtained by dividing by a relatively large speed correction coefficient tVNE (FIG. 16) at the time of high engine speed.₀When the valve timing correction (FIG. 18, step 1811) is performed at low engine speed, this VVTR₀A value VVTR obtained by multiplying by a relatively small correction coefficient tVNE at the time of low rotation is used for control (FIG. 18, step 1810a). For this reason, VVTR used for valve timing correction becomes a relatively small value, and valve timing correction corresponding to the current engine speed can be performed.
[0087]
Thus, according to the present embodiment, it is possible to correct the valve overlap amount more accurately by correcting the detected operating speed of the variable valve timing mechanism in accordance with the engine speed.
[0088]
【The invention's effect】
According to the invention described in each claim, it is possible to reduce the valve overlap amount only when it is really necessary at the time of engine low temperature, and it is possible to prevent an unnecessary decrease in engine output. Play.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment in which a valve timing control device of the present invention is applied to an intake valve of a four-cycle engine.
FIG. 2 is a diagram schematically showing a general opening / closing timing of an intake valve and an exhaust valve.
FIG. 3 is a diagram showing a setting example of basic valve timing values after completion of warming up of the engine.
FIG. 4 is a graph showing a relationship between a valve timing temperature correction amount and an engine coolant temperature.
FIG. 5 is a diagram for explaining a change in pressure in the tank due to a change in fuel temperature.
FIG. 6 is a part of a flowchart showing a fuel property determination routine.
FIG. 7 is a part of a flowchart showing a fuel property determination routine.
FIG. 8 is a graph showing a relationship between a fuel property basic learning value and a tank pressure change.
FIG. 9 is a graph showing correction by a fuel remaining amount of a fuel learning correction coefficient.
FIG. 10 is a flowchart of one embodiment of a valve timing control routine.
FIG. 11 is a graph showing setting of a fuel property correction amount.
FIG. 12 is a flowchart illustrating an embodiment of a correction amount calculation routine based on the variable valve timing mechanism operating speed.
FIG. 13 is a graph showing setting of an operation speed correction amount.
FIG. 14 is a flowchart illustrating an embodiment of a valve timing control routine.
FIG. 15 is a diagram for explaining a change in operating speed of the variable valve timing mechanism depending on the engine speed.
FIG. 16 is a graph showing a relationship between an engine speed and a speed correction coefficient.
FIG. 17 is a flowchart showing a routine for calculating an operation speed correction amount in consideration of the engine speed.
FIG. 18 is a flowchart illustrating an embodiment of a valve timing control routine.
[Explanation of symbols]
1 ... Camshaft
10 ... Variable valve timing device
30 ... Control circuit

Claims (4)

Valve timing control that adjusts the valve overlap amount of the engine according to the operating state of the internal combustion engine by changing the valve timing of the internal combustion engine and sets the valve overlap amount of the engine smaller than the engine high temperature when the engine is cold In the device
An operating speed detecting means for detecting a valve timing changing speed when the valve timing is changed;
An operating speed correcting means for correcting the valve overlap amount at a low engine temperature so that the valve timing changing speed is larger when the valve timing changing speed is larger than when the valve timing changing speed is small;
A valve timing control device for an internal combustion engine comprising: Furthermore, a rotation speed detection means for detecting the engine rotation speed is provided, and a rotation speed correction means for correcting the valve overlap amount at a low engine temperature to be larger when the engine rotation speed is high than when the engine rotation speed is low. The valve timing control device according to claim 1 provided. Furthermore, fuel determination means for determining the properties of the fuel used in the engine,
When it is determined by the fuel determination means that the engine-use fuel is light fuel, the engine valve overlap amount is corrected so as to be larger than when the engine-use fuel is determined to be heavy fuel. Fuel correction means to perform,
The valve timing control device according to claim 1, comprising: The valve timing control device according to claim 3, wherein the fuel determination means determines the property of fuel used in the engine based on a change in fuel temperature in the fuel tank and a change in pressure in the fuel tank after the engine is started.

Images