JP4697485B2 - Start control device for internal combustion engine - Google Patents

Description

  The present invention relates to a start control device for an internal combustion engine that starts by cranking according to a start request.

When starting a reciprocating engine (internal combustion engine) mounted on an automobile (vehicle), the starter is actuated by a start request made by operating a start switch such as an ignition switch or a push switch, and the engine is cranked. Done in
Normally, in order to reduce the load at the start of the engine, when the engine is started, the closing timing of the intake valve is set to a time away from the bottom dead center of the compression stroke toward the top dead center, and the effective compression ratio To reduce the load.

Recently, the intake valve closing timing is set using a variable valve mechanism that varies the opening and closing timing of the intake valve.
By the way, the engine is required to have startability when the outside air temperature is extremely low. Recently, in addition to the usual fuel (gasoline), the startability when using an alcohol mixed fuel (mixed fuel) that is difficult to ignite has been demanded.

However, alcohol-mixed fuel is a fuel that is harder to vaporize than normal fuel (gasoline). For this reason, the engine is difficult to start by setting the closing timing of the intake valve as in the past. In particular, since the fuel mixture ratio of the alcohol-mixed fuel changes every time the fuel is supplied, the startability varies.
For this reason, it is desired that the engine startability is compatible with not only ordinary fuel but also alcohol mixed fuel (0 to 100%).

Therefore, as disclosed in Patent Document 1, a concentration sensor is provided in the fuel tank of an automobile (vehicle), and a variable valve mechanism that varies the closing timing of the intake valve is employed to detect the concentration sensor. In accordance with the alcohol concentration of the fuel in the tank, when the engine is started, the intake valve closing timing is made close to the bottom dead center side by using a variable valve mechanism, and the engine is started. A technique for performing the above has been proposed.
JP 2007-198308 A

In this technology, the timing at which the intake valve is closed is advanced, the actual compression ratio of the cylinder is increased, and the in-cylinder temperature is increased, so that the fuel is easily ignited.
However, the alcohol concentration in the fuel tank differs for each alcohol fuel supply. In addition, the fuel in the path from the fuel tank that is actually used for starting the engine to the engine is often different from the fuel mixture ratio when the fuel is supplied, and the alcohol that is injected into the cylinder when the engine is started. The fuel mixture ratio of the mixed fuel is not certain.

  The technique of Patent Document 1 advances the closing timing of the intake valve to the closing timing set in accordance with the alcohol concentration in the fuel tank while the fuel mixture ratio is not fixed. Tends to be uncertain. Moreover, since the cranking is performed after the closing timing of the intake valve is changed in the technique of Patent Document 1, the load at the time of starting is large, and the means for reducing the initial load is impaired. . In addition, the technique of Patent Document 1 requires a separate sensor for detecting the fuel mixture ratio of the alcohol-mixed fuel, such as detecting the alcohol concentration, and has a large cost burden in addition to uncertainty.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a start control device for an internal combustion engine that can improve startability when a mixed fuel is used with simple control that does not require a sensor.

In order to achieve the above object, the invention according to claim 1 is a variable valve mechanism that varies the closing timing of the intake valve of the internal combustion engine. During the cranking period of the internal combustion engine , the valve closing timing is advanced. A threshold for determining whether or not to perform an angle is set, and when the cranking period exceeds the threshold, the closing timing of the intake valve is advanced step by step by a predetermined amount .
With this configuration, when the internal combustion engine is started, the closing timing of the intake valve is gradually advanced from the normal valve closing timing until cranking is started during cranking. Thus, the actual compression ratio in the cylinder is gradually increased during cranking, and the fuel is easily ignited in the cylinder.

According to the second aspect of the present invention, in order to effectively increase the actual compression ratio in the cylinder, the variable valve mechanism has a timing for closing the valve while keeping the timing for opening the intake valve substantially constant. A variable mechanism is adopted.

According to the first aspect of the present invention, when the internal combustion engine is started, the intake valve is closed during the cranking from the normal valve closing timing until it is started. This makes it easy to ignite (actual compression ratio: large), corresponding to the situation of an internal combustion engine that is difficult to start even with a fuel that is difficult to ignite.
Therefore, the internal combustion engine can be reliably started even in an alcohol-mixed fuel or a cryogenic environment. In addition, an increase in load when starting the internal combustion engine can be suppressed. It is particularly suitable for a mixed fuel in which changes in the fuel mixture ratio are difficult to grasp.

In addition, the startability is ensured only by advancing the closing timing of the intake valve without requiring a sensor, so that the control is simple and the cost is low.
In addition , the closing timing of the intake valve can be advanced only when the advance angle is necessary.
In addition, since the advance angle of the intake valve is stepped by a predetermined amount, the internal combustion engine can be started more reliably even in a fuel that is difficult to ignite or in an extremely low temperature environment.

According to the invention of claim 2 , the actual compression ratio in the cylinder can be effectively increased, and the temperature in the cylinder can be effectively increased.

Hereinafter, the present invention will be described based on a first embodiment shown in FIGS.
FIG. 1 schematically shows a part of an internal combustion engine, for example, a reciprocating SOHC engine 1 capable of using an alcohol mixed fuel (mixed fuel), and a control system of the engine 1.
First, the engine 1 will be described. In FIG. 1, 2 is a cylinder block, and 3 is a cylinder head mounted on the cylinder block 2. Among these, the cylinder block 1 is formed with a cylinder 4 (only a part of which is shown). A piston 6 is housed in the cylinder 4 so as to be able to reciprocate. The piston 6 is connected to a crankshaft 9 provided at the lower part of the cylinder block 2 via a connecting rod 7 and a crankpin 8.

  A combustion chamber 11 is formed on the lower surface of the cylinder head 2. An intake port 12 and an exhaust port 13 are formed on both sides of the combustion chamber 11. Among them, the intake manifold 14 connected to the intake port 12 is provided with a fuel injection valve 15 for injecting fuel. The intake port 12 is provided with an intake valve 17, and the exhaust port 13 is provided with an exhaust valve 18. A spark plug 19 is provided in the center of the combustion chamber 11. A camshaft 22 having both an intake cam 20 and an exhaust cam 21 is provided on the upper portion of the cylinder head 2 via a holding member 23 so as to be rotatable. The camshaft 22 is driven by the shaft output transmitted from the crankshaft 9.

Among the valves, a variable valve mechanism 25 (continuous lift variable valve mechanism) that varies the closing timing of the intake valve 17 is assembled to the intake valve 17. Also, the exhaust valve 18 is assembled with a rocker arm 26 that normally opens and closes the exhaust valve 18 in accordance with the unique valve characteristics, that is, the cam displacement of the exhaust cam 21.
Here, the variable valve mechanism 25 will be described. The mechanism 25 includes a center rocker arm 30 disposed immediately above the intake cam 17, a swing cam 40 disposed immediately above the center rocker arm 30, and the swing cam 40. And a structure in which an intake rocker arm 50 disposed on the side of the intake valve 17 adjacent to the intake valve 17 is combined.

  That is, the center rocker arm 30 is a component that moves up and down in response to the displacement of the intake cam 20. Specifically, the center rocker arm 30 includes, for example, an L-shaped arm portion 31 and a sliding roller 32 provided in the middle of the arm portion 31, and the sliding roller 32 is an intake cam. It is in rolling contact with 17 cam surfaces. An arm end portion 31 a extending in the lateral direction of the arm portion 31 is supported by an outer peripheral portion of a control shaft 34 that is rotatably supported on the intake valve 17 side of the cylinder head 2. Thus, the cam displacement of the intake cam 20 is transmitted to the upper swing cam 40 by the swing displacement of the arm portion 31 with the sliding roller 32 and the arm end portion 31a as a fulcrum. When the center control shaft 34 is rotationally displaced, the center rocker arm 30 is displaced in a direction (advancing or retarding direction) intersecting the axis of the camshaft 22 while changing the rolling contact position with the intake cam 20. To do.

  One end of the swing arm 40 protrudes toward the rocker arm 50, and the other end on the opposite side is rotatably supported by a support shaft 41 provided in the cylinder head 2. A cam surface 42 that pushes the rocker arm 50 is formed on the end surface of the one end. In the lower part, there is provided a sliding roller 43 that is in rolling contact with the inclined surface 35 formed at the end of the arm end 31b extending upward in the center rocker arm 30. As a result, when the center rocker arm 30 is driven, the swing arm 40 swings around the support shaft 41 as a fulcrum. Further, when the rolling contact position of the center rocker arm 30 with respect to the intake cam 20 is changed due to the rotational displacement of the control shaft 34, the posture of the swing cam 40 changes (tilts).

  The rocker arm 50 includes an arm member 51 that is rotationally displaced using the control shaft 34 as a rocker shaft. One end portion of the arm member 51 has an adjusting screw portion 52 that pushes the end of the intake valve 17, and the other end portion has a needle roller 53 that is in rolling contact with the cam surface 42 of the swing arm 40. Thus, when the swing arm 40 swings, the needle roller 53 is pushed or returned by the cam surface 42. Thus, the rocker arm 50 swings around the control shaft 34 as a fulcrum and opens and closes the intake valve 27.

  Here, the cam surface 42 is formed as a base circle section corresponding to the base circle of the intake cam 20 on the upper side, and as a lift section continuous with the base circle section on the upper side, and due to the rotational displacement of the control shaft 34, When the sliding roller 32 of the center rocker arm 30 is displaced in the advance angle direction or the retard angle direction of the intake cam 20, the posture of the swing cam 40 changes, and the region of the cam surface 42 on which the needle roller 53 rolls changes. The ratio between the base section where the needle roller 53 swings and the lift section changes. The valve lift amount of the intake valve 17 is reduced from the low lift caused by the top cam profile of the intake cam 20 due to the change in the ratio of the base section and the lift section with the phase change in the advance direction and the phase change in the retard direction. The intake cam 20 is continuously variable up to the high lift provided by the overall cam profile from the top to the base end. At the same time, the opening / closing timing of the intake valve 17 is varied so that the valve closing timing is larger than the valve opening timing.

That is, as shown in FIG. 2, the variable valve mechanism 25 continuously varies the intake valve 17 from the low lift V1 to the high lift V7. At the same time, the opening / closing timing is continuously varied with the behavior that the valve closing timing is continuously varied while keeping the valve opening timing substantially constant.
And the drive part which drives the control shaft 34, for example, the electric motor 60, is connected to the control part, for example, ECU61 (for example, comprised with a microcomputer). The ECU 61 is also connected to the fuel injection valve 15 and the spark plug 19. The ECU61 be pre information necessary for the operation of the ignition timing in accordance with the operating state of the engine and the fuel injection amount and fuel injection timing and the intake valve controlled variable engine 1, such as the settings (such as maps), is input to the ECU61 The ignition timing, fuel injection amount, fuel injection timing, valve lift amount / opening / closing timing of the intake valve 17 and the like are controlled in accordance with the operating state of the engine (for example, vehicle speed, engine speed, accelerator opening, etc.). It is.

Further, the engine 1 is provided with a start control device 65 including an ECU 61, a variable valve mechanism 25, and a starter that rotationally drives the crankshaft 9, for example, an electric motor 67 (corresponding to the starter of the present application). When the start request signal is output by turning on a start switch connected to the ECU 61, for example, a push start switch 66 (corresponding to the start means of the present application), the start control device 65 operates the electric motor 67 to operate the engine. 1 is cranked, and the engine is started at an ignition timing, fuel injection amount, injection timing, and normal starting opening / closing timing (intake valve) suitable for starting.

In addition to such engine control, the start control device 65 is devised to promote startability of the engine 1. The same device employs a control that exhibits high startability even in a mixed fuel such as an alcohol-mixed fuel that is difficult to ignite, an alcohol-mixed fuel, or even a cryogenic environment.
This control is a technique of advancing the closing timing of the intake valve 17 by the variable valve mechanism 25 during cranking at the time of engine start.

Specifically, a threshold for determining whether or not to advance the valve closing timing of the intake valve 17 in the cranking period is set in the ECU 61. This is determined by, for example, a predetermined time t using a cranking time, and for example, is determined by whether or not the cranking time during cranking has exceeded a predetermined time value t.
Here, the predetermined time value t is a time value when the fuel is ignited and the engine 1 starts when normal fuel (for example, gasoline) is used. It is determined whether or not the fuel injected from the valve 15 is difficult to ignite. For this reason, the threshold value is not the cranking time value, but uses the value of the number of strokes of the engine combustion cycle and the fluctuation of cranking rotation (angular velocity obtained by the crank angle sensor) as the threshold value, which gives the same result. It doesn't matter.

When the cranking period exceeds a threshold value, the ECU 61 operates the electric motor 60 of the variable valve mechanism 25 and closes the intake valve 17 when the cranking time exceeds a predetermined time value t. Control to advance is set (corresponding to the valve closing timing control means of the present application). Specifically, a control is set to advance the closing timing of the intake valve 17 step by step by a predetermined amount. By this control, the timing of closing the intake valve 17 is gradually advanced until the engine 1 is started during cranking, so that the actual compression ratio of the cylinder is increased stepwise. In other words, fuel is easily ignited even in a fuel that is difficult to ignite or in an environment that is difficult to ignite. FIG. 3 shows a flowchart of this control.

Next, the situation when the engine 1 is started will be described based on the flowchart.
For example, assume that the push start switch 66 is turned on and a start request signal is output. At this time, the opening / closing timing of the intake valve 17 is set to a time suitable for starting the engine of normal fuel [the valve closing time is greatly separated from the bottom dead center (BDC) of the compression stroke toward the top dead center (TDC)]. (Α-ray in FIG. 4).

  From this state, the ECU 61 operates the fuel injection valve 15, the spark plug 19, and the electric motor 67 to crank the engine 1. Then, at the initial stage of cranking, the intake valve 17 opens and closes according to the lift curve shown by the thick line α in FIG. 4, that is, at the end far away from the bottom dead center of the compression stroke toward the top dead center, as in normal starting. Is opened and closed as the valve closing timing. The exhaust valve 19 opens and closes according to the lift curve of the exhaust cam 20 indicated by the broken line in FIG.

  Here, as shown in step S1, the ECU 61 determines whether or not the cranking period exceeds a threshold value. For the threshold value, for example, time spent for starting the engine using normal fuel (gasoline) is used. If it is normal fuel and the environment is normal, the process proceeds to step S2 and step S3, and the engine 1 is started only by cranking within a predetermined time value t determined by this time.

At this time, it is assumed that the fuel used for the engine 1 is not a normal fuel and a mixed fuel such as an alcohol mixed fuel whose fuel mixture ratio is difficult to specify is used. Moreover, it is assumed that the engine is in a very low temperature environment (an environment where ignition is difficult). At this time, since the fuel is not sufficiently vaporized in the cylinder, it does not start.
In such a situation where ignition is difficult, the cranking period of the engine 1 becomes long and exceeds the predetermined time value t. Then, the ECU 61 determines that starting cannot be performed in the current situation, and the routine proceeds from step S1 to step S4.

  Then, the ECU 61 controls the variable valve mechanism 25 by the operation of the electric motor 60 to advance the closing timing of the intake valve 17 by a predetermined amount. Specifically, the opening / closing characteristics of the intake valve 17 are the same as shown by the arrows in FIG. 4, the valve opening timing remains substantially constant and the valve closing timing changes to the bottom dead center of the compression stroke. It changes to approach a predetermined amount. When the valve closing timing approaches the bottom dead center of the compression stroke, the actual compression ratio of the cylinder increases and the temperature in the cylinder rises. As a result, the inside of the cylinder becomes an environment in which the fuel is easily vaporized.

This environment promotes the vaporization of the mixed fuel that is difficult to ignite, and the fuel moves from the initial explosion to the complete explosion state. By continuing this complete explosion, the ECU 61 determines that the engine has started (step S3) and ends the start control.
On the other hand, if the start is not confirmed even at the changed closing timing of the intake valve 17, the routine returns to the routine starting from step S1. The ECU 61 again controls the variable valve mechanism 25 to advance the closing timing of the intake valve 17 by a predetermined amount.

  This advance angle is performed in stages until the start of the engine is confirmed. That is, in the latter half of the cranking period, if the engine start is not confirmed, the timing at which the intake valve 17 closes as shown by the lift curve of the thin line β shown in FIG. 4 approaches the bottom dead center of the compression stroke. Continue to advance step by step. During this time, the environment in which the fuel is easily vaporized in the cylinder continues to be increased (temperature increase in the cylinder: large).

As a result, in the later stage of the cranking period, fuel vaporization is promoted even in a mixed fuel such as an alcohol mixed fuel that is difficult to start, or even in an extremely low temperature environment, and the engine 1 is started.
Therefore, the engine 1 can be reliably started even in a fuel that is difficult to start or in an extremely low temperature environment. In particular, since the start control is control for fuel actually supplied to the cylinder, the engine 1 can be reliably started even if the fuel mixture ratio of the alcohol-mixed fuel changes.

Therefore, the startability of the engine can be improved. It is particularly suitable when using a mixed fuel in which changes in the fuel mixture ratio are difficult to grasp. In addition, since it is possible to prevent the cranking period from becoming unnecessarily long, the starting fuel can be reduced. In addition, the start control is simple because the timing of closing the intake valve 17 is advanced during cranking until the complete explosion of the fuel is confirmed. In addition, at the start of cranking, the closing timing of the intake valve 17 may be the same as before, so that the starting load can be suppressed and the characteristics of easy starting can be saved. Furthermore, since no sensor is required, the cost burden can be reduced. In addition, even if the intake valve 17 is changed to the late closing side at the initial stage of the cranking period, the startability is ensured. Therefore, the mirror cycle by the late closing of the intake valve 17 is advanced, and the engine There is also an advantage that fuel consumption can be reduced.

In particular, the variable valve mechanism 25 can effectively increase the actual compression ratio in the cylinder by adopting a mechanism that varies the valve closing timing while making the timing of opening the intake valve 17 substantially constant. The temperature in the cylinder can be effectively increased, and the engine can have high startability.
In addition, since a threshold for determining whether or not to advance the valve closing timing is set for the start control, and when the cranking period exceeds the threshold, control for advancing the valve closing timing of the intake valve 17 is adopted. Only when the advance angle is required, the closing timing of the intake valve 17 can be advanced, and the advance angle control can be performed effectively. In addition, if the advance angle of the intake valve 17 is advanced step by step, the engine 1 can be started more reliably even in any fuel that is difficult to start or in an extremely low temperature environment.

5 and 6 show a second embodiment of the present invention.
This embodiment does not use the continuous lift variable valve mechanism that continuously varies both the valve lift and the valve opening / closing timing as in the first embodiment as the variable valve mechanism. The continuous phase variable valve operating mechanism 70 that continuously varies the phase of the valve is used (applied to the DOHC engine).

  That is, the mechanism 70 is provided with an advance chamber 74 and a retard chamber 75 in a short cylindrical housing 73 having an intake cam sprocket 72, for example, and between the advance chamber 74 and the retard chamber 75 for intake. The vane 75 connected to the cam shaft 22a is provided, and the vane 75 is displaced from the retard chamber 74 to the advance chamber 75 by supplying hydraulic pressure, so that the phase of the intake cam 20 is retarded or advanced. To do.

By using this continuous phase variable valve mechanism 70, as shown in FIG. 6, during cranking of the engine, the phase of the intake valve 17 is changed from, for example , a thick line α in the early cranking period to a thin line β in the late cranking period. By changing in this way, the timing at which the intake valve 17 is closed may be advanced.
7 and 8 show a third embodiment of the present invention.

In the present embodiment, a variable valve mechanism 80 that continuously varies the valve opening period of the intake valve 17 is used as a variable valve mechanism (applied to a DOHC engine).
The mechanism 80 continuously changes the valve opening period of the intake valve 17 by changing the constant rotation of the intake camshaft 10 to non-uniform rotation.
In other words, the mechanism 80 externally fits the cam lobe 82 having the intake cam 20 to the outer peripheral surface of the intake cam shaft 22a. Further, the rotation of the camshaft 22 a is transmitted to the cam lobe 82 by changing the speed at a predetermined cycle by an inconstant speed mechanism 84 using a harmonic ring 83. The harmonic gear 85 controls the eccentric phase of the harmonic ring 83 to continuously vary the speed at which the intake cam 20 passes through the proximal end portion of the intake valve 17.

Using this continuous opening period variable valve operating mechanism 80, during cranking of the engine as shown in FIG. 8, cranking period the valve opening period, for example from cranking period early bold line α of the intake valve 17 The timing at which the intake valve 17 closes may be advanced by changing it as shown by the latter thin line β.
In addition, this invention is not limited to any embodiment mentioned above, You may implement in various changes within the range which does not deviate from the main point of this invention.

The figure which shows the control system of the starting control apparatus which concerns on the 1st Embodiment of this invention with a part of cylinder head. The diagram for demonstrating the characteristic of the variable valve mechanism mounted in the engine. The flowchart for demonstrating control of a starting control apparatus. The figure for demonstrating when an intake valve advances during cranking at the time of engine starting. The perspective view explaining the variable valve mechanism of a different form used as the principal part of the 2nd Embodiment of this invention. The figure for demonstrating when an intake valve advances an angle during cranking of an engine with the variable valve mechanism. The perspective view explaining the variable valve mechanism of a different form used as the principal part of the 3rd Embodiment of this invention. The figure for demonstrating when an intake valve advances an angle during cranking of an engine with the variable valve mechanism.

Explanation of symbols

17 Intake valve 25 Variable valve mechanism 61 ECU (valve closing timing control means)
66, 67 Electric motor, push start switch (starting means)

Claims (2)

When the internal combustion engine is requested to start, starting means for starting the internal combustion engine by cranking while opening and closing the intake valve;
A variable valve mechanism for varying the closing timing of the intake valve of the internal combustion engine;
A valve closing timing control means for controlling the variable valve mechanism so as to advance the closing timing of the intake valve during the cranking ;
The valve closing timing control means sets a threshold value for determining whether or not to advance the valve closing timing in the cranking period. When the cranking period exceeds the threshold value, the valve closing timing control means determines the closing timing of the intake valve. An internal combustion engine start control apparatus , wherein the variable valve mechanism is controlled so as to be advanced step by step by a predetermined amount . 2. The start control device for an internal combustion engine according to claim 1, wherein the variable valve mechanism changes a valve closing timing while keeping a timing at which the intake valve opens substantially constant. 3. .

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