JP2006348774A - Intake control device for engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure good startability even under a cold condition in an engine provided with a variable lift mechanism VVL capable of lifting intake valves 1, 2 by rocking cams 4, 5 and continuously changing lift by changing rocking angle of the rocking cams 4, 5, and increasing lift and retarding close timing of the intake valves 1, 2. <P>SOLUTION: At a time of cold start, lifts of the intake valves 1, 2 are minimized and cranking is started under a condition where rotary resistance is low (steps S3, S4). After oil film is formed on a sliding part of the variable lift mechanism by cranking, lift of the intake valves 1, 2, filled quantity of intake air to a cylinder is increased to increase effective compression ratio and to enhance intake air flow in the cylinder, evaporation and atomization of fuel and mixing with air are promoted (step S12). Consequently, reduction of cranking resistance, ignitability of air fuel mixture and improvement of combustibility are compatibly materialized with appropriate balance and good startability is secured even under the cold condition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an intake control device for an engine in which the lift amount of an intake valve is changed in accordance with the operating state of the engine, and particularly belongs to the field of control technology at the time of engine start.

  2. Description of the Related Art Conventionally, as disclosed in, for example, Japanese Patent Application Laid-Open No. H10-260260, there has been known an engine valve system that is provided with a variable lift mechanism that continuously changes the lift amount and opening / closing timing of an intake valve. In this device, the operation of the eccentric cam of the intake side camshaft is transmitted to the swing cam via a link, and the intake valve is opened and closed by this swing cam. Then, the swing range of the swing cam is changed by changing the position of the fulcrum of the link, whereby the lift amount of the intake valve and the like are continuously changed.

  Thus, by continuously changing the lift amount of the intake valve, etc., the cylinder can be filled with a necessary amount of air corresponding to the operating state (load and rotation speed) of the engine. It is possible to control the valve so that it is fully open or close to the opening in the most operating range, or to eliminate the throttle valve, thereby reducing pumping loss and reducing fuel consumption.

  However, since the variable lift mechanism as described above has a complicated structure and increases the number of mechanical sliding portions, the frictional resistance to the operation tends to increase. In particular, when a swing cam is used, the frictional resistance tends to increase when the direction of rotation changes.

  In particular, when cranking is started at the time of starting, since the oil film is not sufficiently formed in many of the sliding portions of the lift variable mechanism, the frictional resistance is further increased in each of the sliding portions, Thus, coupled with the large number of sliding parts, the rotational resistance against cranking becomes considerably large, and the engine startability may be reduced.

  However, if the lift amount of the intake valve is reduced by taking advantage of the characteristics of the variable lift mechanism, even if the mechanism has many sliding parts as described above, the frictional resistance is equivalent to that of a normal valve system, or Rather it can be made smaller. Thus, for example, in the engine disclosed in Patent Document 2, the variable valve mechanism is controlled in advance so as to achieve a small lift when the engine is stopped, thereby reducing the rotational resistance at the time of subsequent engine start and starting performance. To ensure.

In Patent Document 2, the crankshaft is reversely rotated by a predetermined angle before starting as a countermeasure against a failure in which the engine has stopped with a large lift due to a delay in control response, actuator sticking, or the like. Thus, a technique has been proposed in which cranking is started in a state where the frictional resistance of the sliding portion due to the reaction force of the valve spring is relatively small.
JP 2004-301058 A JP 2004-257255 A

  By the way, when the lift amount of the intake valve at the time of cranking is reduced as in the engine of Patent Document 2, the rotational resistance against cranking can be reduced, but as the lift amount decreases, the lift to the cylinder is reduced. Since the amount of intake charge is reduced, the effective compression ratio is reduced, and the intake air flow in the cylinder is also weakened, which makes it difficult to promote vaporization of fuel and mixing with air.

  In particular, when the lift amount of the intake valve is changed by changing the swing range of the cam as in Patent Documents 1 and 2, normally, the valve opening period becomes narrower as the lift amount decreases. Therefore, if the lift amount is reduced until the rotational resistance against cranking becomes sufficiently small, the intake valve closes in the middle of the intake stroke of the cylinder. Decrease and weakening of intake flow are remarkable.

  For this reason, for example, when the engine is not warmed up and the temperature around the cylinder and the intake system is low and the fuel vaporization and atomization are originally poor (so-called cold start), the ignitability of the air-fuel mixture In addition, the combustibility becomes considerably low, and furthermore, when the engine is cold, the rotational resistance of the entire engine may naturally increase, and the startability may not be ensured.

  In other words, in an engine equipped with a variable lift mechanism as described above, there is a risk that the rotational resistance against cranking may be larger than that with a normal valve system, and if the lift amount is reduced so as not to do so, In this case, since the ignitability and combustibility of the air-fuel mixture are deteriorated, it is difficult to ensure startability in the cold state.

  The present invention has been made in view of the above-described problems, and particularly pays attention to the fact that the rotational resistance increases when the oil film is not sufficiently formed at each sliding portion of the variable lift mechanism at the start of cranking. Thus, by devising the control procedure of the lift amount of the intake valve during cranking, it is to ensure good startability even in the cold.

  In order to achieve the above object, according to the present invention, when starting the engine, first, the lift amount of the intake valve is reduced, and cranking is started with a small rotational resistance. The lift amount is increased after promoting the formation of an oil film in the part.

  That is, the invention of claim 1 is provided with a variable lift mechanism capable of continuously changing the lift amount of the intake valve lifted by the swing cam by changing the swing range of the swing cam. An intake control device for an engine is assumed on the assumption that the variable lift mechanism is controlled based on at least the operating state of the engine.

  And, when the lift variable mechanism is to change its lift characteristic so that the valve opening period is widened with the increase of the lift amount of the intake valve and the closing timing is delayed, It is assumed that there is provided a lift control means for controlling the variable lift mechanism so that the intake valve is in a predetermined small lift state that is closed during the intake stroke of the cylinder, and the lift amount is increased during the subsequent cranking.

  In the above configuration, first, due to the characteristics of the variable lift mechanism, when the lift amount of the intake valve is relatively small, the valve opening period (crank angle) is also narrowed, and the closing timing is relatively early (advanced side). Therefore, in an operating state where the output demand to the engine is low, a small lift is used, and the intake valve is made to have a so-called early intake closing characteristic in which the intake valve is advanced from the bottom dead center of the cylinder, that is, during the intake stroke. This makes it easier to reduce cylinder pumping loss.

  On the other hand, since the valve opening period becomes longer when the lift amount is relatively large, it is easy to secure the time for filling the intake air, and the closing timing of the intake valve is retarded. After that, it becomes easy to open, and in this way, the charging efficiency can be increased by the inertia of the intake air flow.

  Further, when the engine is started, the variable lift mechanism is controlled by the lift control means. First, the lift amount of the intake valve is set to a relatively small state (small lift state). As a result, even when the oil film is not sufficiently formed on each sliding part of the variable lift mechanism, the frictional resistance does not become excessively large, and cranking starts with a relatively small resistance. Is done.

  At that time, the smaller the lift amount, the smaller the rotational resistance and smooth cranking becomes possible, but due to the basic characteristics of the variable lift mechanism described above, the opening period of the intake valve becomes narrower with a small lift. Since it closes in the middle of the intake stroke of the cylinder, the amount of intake charge to the cylinder is considerably reduced.

  On the other hand, when cranking is started as described above, the formation of an oil film is also promoted at each sliding portion of the variable lift mechanism, and the frictional resistance is further reduced. Even if it is increased, this does not increase the rotational resistance of the engine excessively.

  Therefore, by controlling the variable lift mechanism by the lift control means, the lift amount of the intake valve is increased during cranking, thereby increasing the charge amount of intake air into the cylinder and increasing the effective compression ratio, The intake air flow can also be strengthened to promote vaporization of fuel and mixing with air.

  In this way, it is possible to achieve both a reduction in rotational resistance against cranking and an improvement in the ignitability of the air-fuel mixture in the cylinder and an improvement in combustibility at the start of the engine, so that good startability even in cold conditions. Can be secured.

  More specifically, for example, the variable lift mechanism is controlled so that the lift amount of the intake valve is minimized until the crankshaft of the engine is rotated at least once by cranking. Then, the lift amount of the intake valve may be increased so that the closing timing of the intake valve is gradually retarded according to the rotation of the crankshaft and approaches the bottom dead center of the cylinder ( Invention of Claim 2).

  In this way, first, the rotational resistance at the start of cranking can be made sufficiently small by minimizing the lift amount of the intake valve, and if the crankshaft makes one revolution, engine oil is put in each sliding portion. Since the frictional resistance is surely reduced by turning, the lift amount of the intake valve is increased according to the rotation of the crankshaft so that the closing timing approaches the bottom dead center of the cylinder. The intake charge amount can be effectively increased and the in-cylinder flow can be enhanced.

  More preferably, it further comprises a determination means for determining the temperature state of the engine, and when the lift control means increases the lift amount of the intake valve during cranking for starting as described above, According to the determined engine temperature state, the variable lift mechanism is controlled so that the degree of increase in the lift amount increases as the temperature decreases (invention of claim 3).

  In this way, the degree of increase in the lift amount of the intake valve during cranking changes depending on the temperature state at the time of engine start, and the lift amount increases as the temperature becomes lower and the fuel vaporization atomization becomes worse. On the other hand, when the temperature is not so low, the lift amount is not so large.

  In other words, by carefully changing the lift amount of the intake valve in consideration of the engine temperature at the time of starting, the lift amount can be increased to the minimum necessary to ensure the ignitability and combustibility of the air-fuel mixture and lift up Since the increase in rotational resistance associated with can be suppressed as much as possible, the engine can be started more smoothly.

Next, in the invention of claim 4, as in the invention of claim 1, the lift amount of the intake valve lifted by the swing cam is continuously changed by changing the swing range of the swing cam. In an intake control device for an engine in which a variable lift mechanism is provided, and the variable lift mechanism is controlled based on at least the operating state of the engine, the variable lift mechanism opens as the lift amount of the intake valve increases. When the lift characteristics are changed so that the period is extended and the closing timing is delayed,
Determination means for determining the temperature state of the engine, and at the time of starting the engine, first, the variable lift mechanism is controlled so that the intake valve is in a predetermined small lift state that is closed during the intake stroke of the cylinder, and then the determination means If the engine temperature state determined by the above is an unwarmed state that is lower than a predetermined temperature, the lift amount of the intake valve increases during cranking, and if the engine is not unwarmed, the lift amount is substantially constant. And a lift control means for controlling the variable lift mechanism.

  With the above configuration, if the engine is in an unwarmed state at the start (that is, during a cold start), the same action as that of the invention of claim 1 can be obtained, and a good startability can be ensured even in a cold state. . On the other hand, if it is not cold, the intake valve is kept in a small lift amount from the start of cranking to the complete explosion state, and the rotational resistance is reduced, so the engine can be started more smoothly. Can do.

  In this case as well, the lift control means controls the variable lift mechanism so that the lift amount of the intake valve is minimized until the crankshaft makes at least one rotation, as in the inventions of the second and third aspects. After that, if the engine is not warmed up, the lift amount of the intake valve is increased so that the closing timing of the intake valve gradually retards and approaches the bottom dead center of the cylinder according to the rotation of the crankshaft. (5). Alternatively, the lift control means may control the variable lift mechanism so that the degree of increase in the lift amount of the intake valve increases as the temperature decreases, according to the engine temperature state determined by the determination means (claims). Item 6).

  Furthermore, the lift control means may control the variable lift mechanism so that the degree of increase in the lift amount of the intake valve increases during the cranking. In this way, after engine oil has sufficiently turned to each sliding portion of the variable lift mechanism, the lift amount of the intake valve can be rapidly increased, and the intake charge amount to the cylinder can be increased in a short time. Even when the temperature is particularly low, such as on the ground, the startability can be secured by increasing the ignitability and combustibility of the air-fuel mixture while reducing the rotational resistance against cranking.

In the above-described intake control device, a phase variable mechanism that can continuously change the phase angle of the lift of the intake valve, and when the engine is in the idle operation range, the intake valve is in a lift peak state in the middle of the intake stroke of the cylinder. And a phase control means for controlling the phase variable mechanism so that the phase angle is advanced from the idle operation range when the partial load operation region is adjacent to the high load side of the idle operation range. Well, in that case, if the lift control means is not warmed up when the engine is started, the lift control means increases the lift amount of the intake valve until the closing timing of the intake valve is retarded from that during the idling operation. It is preferable to let it be. (Claim 8)
That is, generally in the idling state, the lift amount of the intake valve is reduced in the same manner as when cranking is started, so that the intake valve closes in the middle of the intake stroke of the cylinder, and the flow in the cylinder is weakened. There is a risk that the combustion stability may be reduced due to the above. Therefore, in the above-described configuration, the phase angle of the intake valve lift is retarded during idling by control of the phase variable mechanism by the phase control means, and the intake valve enters a lift peak state in the middle of the intake stroke with the highest intake efficiency. By doing so, weakening of the in-cylinder flow can be suppressed and the required combustion stability can be obtained.

  In that case, when the engine is cold-started, the intake valve lift amount until the closing timing of the intake valve is further retarded than when idling with the lift phase angle retarded as described above. By increasing the value, the amount of intake air charged into the cylinder can be sufficiently increased, and the in-cylinder flow can be sufficiently enhanced.

  As described above, according to the intake control device for an engine according to the present invention, in an engine having a variable lift mechanism capable of continuously changing the lift amount of the intake valve, the lift amount of the intake valve is first set at the start. Cranking is started with a small rotational resistance, thereby promoting the formation of an oil film at each sliding portion of the variable lift mechanism, and by increasing the lift amount, the rotational resistance against cranking is increased. Reduction and improvement of the ignitability of the air-fuel mixture in the cylinder and improvement of combustibility can be achieved with an appropriate balance, and good startability can be ensured even in the cold.

  The lift amount of the intake valve to be increased during cranking is finely controlled so that the increase degree of the lift amount changes according to the engine temperature at the start (Claims 3 and 6). While ensuring the ignitability and combustibility of the air-fuel mixture, the engine can be started more smoothly by suppressing an increase in rotational resistance.

  Further, when the engine is not in an unwarmed state at the time of starting, that is, in the case of a warm start, the lift amount of the intake valve is not increased during cranking but is maintained in a small lift state (claim 4). ), The rotational resistance can be reduced and the engine can be started smoothly.

  Further, if the degree of change is changed in the middle of increasing the lift amount of the intake valve during cranking (Claim 7), good startability can be ensured even in cold regions.

Furthermore, a variable phase mechanism that can continuously change the phase angle of the intake valve lift is provided, and the required idle stability is obtained by retarding the phase angle of the lift of the intake valve while maintaining a small lift during idling. In addition, when the engine is cold started, by increasing the lift amount until the closing timing of the intake valve is further retarded than when idling with the phase angle retarded as described above, The effect of the above-described invention becomes more reliable (claim 8).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

  FIG. 1 shows a configuration of an intake side valve system of an engine according to an embodiment to which the present invention is applied. Although not shown, this engine is an in-line four-cylinder engine in which four cylinders are arranged in a line, and each cylinder has two intake valves 1 and 2 and two exhaust valves (not shown). A 4-valve double overhead cam system is used. In the figure, reference numeral 3 denotes an intake side cam which is arranged so as to extend in the longitudinal direction of the engine in which the four cylinders are arranged, and is rotationally driven by a crankshaft of the engine via a cam chain (not shown). It is a shaft.

  A known phase variable mechanism 18 (Variable Cam Timing: hereinafter abbreviated as VCT) capable of changing the rotational phase of the camshaft 3 relative to the crankshaft within a predetermined angle range is attached to the front end portion of the camshaft 3. Has been. Although not described in detail, the VCT 18 includes a rotor fixed to the front end of the camshaft 3 that passes through the center hole of the sprocket 19 and a casing that is disposed so as to cover the rotor from the front of the engine and is fixed to the sprocket 19. A plurality of hydraulic working chambers are formed between the rotor and the casing side by side in the circumferential direction.

  Then, the direction and magnitude of the operating hydraulic pressure to the VCT 18 are changed by the solenoid valve 20 duty-controlled by the controller 17, the rotor and the casing are rotated relative to each other, and the rotation phase of the camshaft 3 relative to the crankshaft changes. Thus, the opening / closing timing of the intake valves 1 and 2 as viewed from the crank angle, that is, the lift phase angle of the intake valves 1 and 2 can be continuously changed.

  The rotor is biased in the direction opposite to the rotation direction (retarded side) with respect to the casing by, for example, a spring member or the like, so that the lift phase of the intake valves 1 and 2 when the hydraulic pressure is not supplied. The angle is the maximum retardation (advance amount 0 °).

  On the camshaft 3, a pair of swing cams 4 and 5 are supported swingably for each cylinder. The pair of swing cams 4, 5 are arranged so as to correspond to the two intake valves 1, 2, respectively, and are connected to each other by a cylindrical connecting portion 9 so as to swing integrally around the camshaft 3. It is supposed to be. As a result, the two intake valves 1 and 2 are lifted simultaneously for each cylinder. The outer peripheral surface of the connecting portion 9 is a cam journal portion that is in sliding contact with the cam bearing surface.

  In order to operate the swing cams 4 and 5 as described above, the camshaft 3 has four circular eccentric cams 6 that are eccentric from the axis X (the rotation center of the camshaft 3: see FIG. 2 and the like). They are integrally provided with a space therebetween. An outer ring 7 is fitted on each eccentric cam 6 so as to be rotatable. The swing cam 5 is connected to an eccentric convex portion provided so as to protrude from the outer periphery of the outer ring 7 via a connecting link 8. It is connected. That is, one end side of the outer ring 7 is rotatably fitted to the eccentric cam 6 of the camshaft 3, and the other end portion (eccentric convex portion) is connected to the swing cam 5 by the connecting link 8 (hereinafter, referred to as “the outer ring 7”). This is called an offset link).

  A control shaft 11 is provided in parallel with the camshaft 3 obliquely above. Four control arms 12 are coupled and fixed to the control shaft 11, and the distal end portion of each control arm 12 and the other end portion of the offset link 7 are connected by a regulation link 13. The restriction link 13 restricts the displacement of the offset link 7 and reciprocates the other end when the one end side of the offset link 7 revolves around the camshaft 3 as the eccentric cam 6 rotates. Thus, the connecting link 8 connected to the other end of the offset link 7 swings the swing cams 4 and 5.

  Further, the control shaft 11 is coupled with a worm gear 14 having teeth formed on only a part of its circumference, and a worm 16 that is rotationally driven by an electric motor 15 meshes with the teeth of the worm gear 14. . Then, the motor 15 is actuated in response to the input of the control signal from the controller 17 and the control shaft 11 is rotated to change the position of the control arm 12, whereby the reciprocating motion of the other end of the offset link 7 is performed. The trajectory, that is, the swing trajectory of the connecting link 8 is changed, thereby changing the swing angle (swing range) of the swing cams 4 and 5, the lift amount of the intake valves 1 and 2, the opening / closing timing, etc. The lift characteristics are changed.

  In other words, the connecting link 8 and the restriction link 13 connect the swing cam 5 and the offset link 7 and also operate the offset link 7 accompanying the rotation of the eccentric cam 6 with the swing cam 5 (and the swing link 5). A link mechanism that restricts the moving cam 4) to swing is configured. Further, including the link mechanism, a variable lift mechanism capable of continuously changing the lift amount of the intake valves 1 and 2 by the eccentric cam 6, the offset link 7, the control shaft 11, the control arm 12 and the like of the cam shaft 3. (Variable Valve Lift: hereinafter also referred to as VVL).

  More specifically, the configuration of the VVL is as follows. First, as shown in FIG. 2 (b), a direct acting tappet 21 is provided at the upper end of the stem of the intake valve 2, and the swing cam 5 is applied to the tappet 21. It touches. In the intake valve 2, the intake port 25 is closed by a valve spring 24 provided between a retainer 22 provided in the tappet 21 and a retainer 23 provided in the cylinder head (intake valve 1, 2 lift direction). (Opposite direction). Note that the intake valve 1 has the same configuration as the intake valve 2.

  One end portion of the connection link 8 is rotatably connected to the swing cam 5 by a pin 31, while one end portion of the regulation link 13 is rotatably connected to a tip portion of the control arm 12 by a pin 32. ing. Thus, the connecting link 8 and the regulating link 13 are disposed on both sides of the offset link 7 and are linked with the offset link 7 interposed therebetween. That is, the other end of each of the connection link 8 and the restriction link 13 is connected to the other end of the offset link 7 coaxially and rotatably by the connection pin 33. The pins 31 to 33 all extend parallel to the camshaft 3.

  As shown in the figure, the connecting pin 33 between the offset link 7 and the connecting link 8 is located above the camshaft 3, and the rotation center of the control arm 12 (the axis of the control shaft 11) is located on the side of the connecting pin 33. positioned. The pin 32 at the tip of the control arm 12 is a rotation shaft of the restriction link 13, and by changing the position of the pin 32, the swing trajectory of the restriction link 13 and the connecting pin 33 is changed. , 2 can be changed.

  That is, the specific operation of each link or pin will be described in detail below. The control shaft 11 and the control arm 12 are rotated by the motor 15 so that the pin 32 is moved below the control shaft 11 as shown in FIG. In this case, the swing angle of the swing cams 4 and 5 becomes large, and the lift amount of the intake valves 1 and 2 at the lift peak becomes the largest lift control state. Further, when the pin 32 is moved upward by the rotation of the control arm 12 or the like, the swing angle of the swing cams 4 and 5 is reduced accordingly, and the pin 32 is moved to the camshaft as shown in FIG. If it is positioned above 3, the lift amount of the intake valves 1 and 2 becomes the smallest lift control state.

  In the large lift control state shown in FIG. 2, the swing cam 5 presses the direct acting tappet 21 on the tip side of the cam nose as shown in FIG. A lift peak state (a state where the swing cam 4 greatly lifts the intake valve 1 via the direct acting tappet) and a intake valve 2 (the intake valve 1) as shown in FIG. Oscillates between zero lift and no lift. Similarly, in the case of FIG. 3 which is a small lift control state, it swings between a lift peak state (pressing the tappet 21 on the base end side of the cam nose) and a zero lift state (FIGS. 3A and 3B). reference).

(Operation of variable lift mechanism)
Hereinafter, the operation of such links and cams will be described in detail with reference to FIGS. In both figures, the control arm 12, the connecting link 8, and the restricting link 13 are simply represented by straight lines, and the rotation trajectory of the center of the eccentric cam 6 (the center of the outer ring of the offset link 7) is indicated as T0. ing. As described above, the relationship between the intake valve 1 and the swing cam 4 is the same as the relationship between the intake valve 2 and the swing cam 5, and the swing cam 4 works in the same manner as the swing cam 5. Now, the relationship between the intake valve 2 and the swing cam 5 will be described.

  First, the profile of the oscillating cam 5 itself will be described with reference to FIG. 4. The circumferential surface of the oscillating cam 5 has a base circle surface (base circle section) θ1 having a constant radius of curvature within a predetermined angular range, A cam surface (lift section) θ2 having a gradually increasing radius of curvature is formed following θ1. The figure shows the large lift control state of FIG. 2, and the control arm 12 is in the large lift control position.

  The solid line in FIG. 2 shows the state of FIG. 2B in which the intake valve 2 is in the vicinity of the lift peak. At this time, the pin 31 is pulled up most by the connecting link 8, and the swing cam 5 is The cam nose tip side of the surface θ2 is in contact with the tappet 21. On the other hand, the phantom line shows a zero lift state (FIG. 2A). At this time, the base circle surface θ1 of the swing cam 5 is in contact with the tappet 21, and the intake valve 2 is not lifted (intake air). Valve 2 is closed).

  When the camshaft 3 (eccentric cam 6) rotates in the clockwise direction in the figure, one end side (lower end side in the figure) of the offset link 7 moves along the axis X of the camshaft 3 as indicated by the arrow in the figure. In this case, the displacement of the other end of the offset link 7 is regulated by the regulation link 13 connected thereto. That is, the restriction link 13 swings between the position of the solid line and the position of the phantom line around the pin 32 positioned below the control shaft 11, and accordingly, the other end side of the offset link 7. The (connecting pin 33) reciprocates around the pin 32 every time the eccentric cam 6 makes one revolution (the movement locus of the connecting pin 33 is shown as T1).

  With the reciprocating arc motion T1 of the connecting pin 33, the other end portion (pin 31) of the connecting link 8 whose one end portion is connected to the offset link 7 by the same connecting pin 33 is reciprocated along a locus shown as T2. The oscillating cam 5 that is circularly moved and is connected to the connecting link 8 by the pin 31 oscillates between the position of the solid line and the position of the phantom line in the figure. That is, when the connecting pin 33 moves upward, the pin 31 is pulled upward by the connecting link 8, and the cam nose of the swing cam 5 pushes down the tappet 21, thereby pushing the valve spring 24 (see FIG. 2). The intake valve 2 is lifted while shrinking.

  On the other hand, when the connecting pin 33 moves downward, the pin 31 is pushed downward by the connecting link 8 and the cam nose of the swing cam 5 rises. Therefore, the valve spring 24 compressed as described above. The tappet 21 is pushed up by the reaction force and moves upward so as to follow the rise of the cam nose. The intake valve 2 is pulled up by the retainer 22 in the tappet 21 and the intake port 25 is closed.

  That is, in the large lift control state, the swing cam 5 swings greatly so as to press the tappet 21 by substantially the entire base circle surface θ1 and cam surface θ2 of the peripheral surface, and thus corresponds to such a large swing angle. As a result, the lift amount of the intake valve 2 increases.

  Next, when the control arm 12 is turned upward from the large lift control state until it becomes substantially horizontal around the axis of the control shaft 11, as shown in FIG. 3 and FIG. The pin 32, which is the moving shaft, is positioned on the near side in the rotational direction of the camshaft 3 with respect to the large lift control state, and the small lift control state with a small lift amount is entered. In FIG. 5 as well, the state where the intake valve 2 is in the vicinity of the lift peak is indicated by a solid line, and the state of zero lift is indicated by a virtual line as in FIG.

  In this figure, when the camshaft 3 (eccentric cam 6) rotates, the displacement of the connecting pin 33 of the offset link 7 is restricted by the restricting link 13 and is located on the side of the control shaft 11 as in the large lift control state. A reciprocating arc motion T3 is performed around the pin 32 (the restriction link 13 reciprocates between the solid line position and the virtual line position in the figure). The pin 31 of the connecting link 8 performs a reciprocating arc motion T4 in accordance with the reciprocating arc motion T3 of the connecting pin 33, and the swing cam 5 connected to the connecting link 8 by the pin 31 is indicated by a solid line in the figure. The intake valve 2 is opened and closed by swinging between the position and the position of the virtual line.

  That is, in the small lift control state, the swing angle of the swing cam 5 is smaller than that in the large lift control state, and the swing cam 5 has a base circle surface θ1 on its peripheral surface and a cam surface continuous therewith. The tappet 21 is pressed only by a part of θ2, and the lift amount of the intake valve 2 is reduced.

(Change in lift characteristics)
FIG. 6 shows the lift curves of the intake valves 1 and 2 that are continuously changed from the large lift control state to the small lift control state by the operation of the variable lift mechanism VVL as described above. In the drawing, a lift curve L1 indicates a large lift control state in which the swing cam 5 swings between the solid line position (near the lift peak in the large lift control state) and the virtual line position (zero lift) in FIG. L2 shows a small lift control state in which the swing cam 5 swings between the solid line position (near the lift peak in the small lift control state) and the virtual line position (zero lift) in FIG.

  As shown in the figure, according to the lift variable mechanism VVL of this embodiment, as the lift amount of the intake valves 1 and 2 increases, the valve opening period (the crank angle period from the opening timing to the closing timing, not including the buffer section). ) Also spreads, and the closing timing of the intake valves 1 and 2 is delayed. This is because, as described above, the lift amount of the intake valves 1 and 2 is changed in accordance with the change in the swing angle of the swing cam.

  In the example of the figure, the lift peak timing (crank angle position) is advanced as the lift amount of the intake valves 1 and 2 is smaller. As described above, in the transition from the large lift control state to the small lift control state, the position of the restriction link 13 is moved to the front side in the rotational direction of the camshaft 3 by the rotation of the control arm 12 or the like. This is because the trajectory of the reciprocating arc motion of the connecting pin 33 moves from the position T1 in FIG. 4 to the position T3 in FIG.

  That is, in the large lift control state shown in FIG. 4, the center of the eccentric cam 6 when the intake valves 1 and 2 are in the vicinity of the lift peak is located at the point Ta on the rotation locus T0. In the small lift control state shown in FIG. 2, the center position of the eccentric cam 6 in the vicinity of the lift peak moves to a point Tb shown in FIG. That is, when shifting from the large lift control state to the small lift control state, the lift peaks of the intake valves 1 and 2 advance by the center angle θ3 of the points Ta and Tb on the rotation locus T0 as shown in FIG. is there.

  In short, according to the variable lift mechanism VVL of this embodiment, the lift characteristics of the intake valves 1 and 2 are such that the smaller the lift amount, the narrower the valve opening period, that is, the lift operating angle, and the earlier the closing timing. On the other hand, the valve opening period increases with a continuous increase in the lift amount, and the closing timing changes so as to be retarded.

  Such a change in lift characteristics is consistent with general engine intake characteristics. That is, in general, the engine load is often increased on the high rotation side, but on the high rotation side, even if the valve opening periods of the intake valves 1 and 2 are the same as viewed from the crank angle, Since the interval is shortened, it is desirable not only to increase the intake passage cross-sectional area by increasing the lift amount, but also to secure time for intake by increasing the valve opening period (crank angle). Further, if the closing timing of the intake valves 1 and 2 is retarded until after the bottom dead center of the cylinder, the charging efficiency can be increased by the inertia of the intake flow.

  On the other hand, in order to reduce the pumping loss of the cylinder, it is preferable that the intake valves 1 and 2 be closed in the middle of the intake stroke of the cylinder, so that the so-called early intake closing characteristic is used. In this case, the lift amount of the intake valve should be reduced and the phase angle should be advanced.

  By continuously changing the lift amount of the intake valves 1 and 2 from the minimum lift to the maximum lift by the VVL having the characteristics as described above, in the engine of this embodiment, the output request to the engine can be made without depending on the throttle valve. A corresponding amount of air can be filled into the cylinder, thereby controlling the output of the engine. Therefore, in this engine, although not shown, although a motor-driven throttle valve is arranged upstream of the intake passage to each cylinder, this is normally fully opened even in a partial load region to reduce the pumping loss of the cylinder. As a result, fuel consumption is reduced.

  More specifically, in this embodiment, the lift amount of the intake valve by the lift variable mechanism VVL as described above is basically changed in accordance with the operating state of the engine. For example, referring to a control map as shown in FIG. 7, an appropriate lift amount corresponding to the engine target torque (engine load state) and the engine speed is obtained as a control target value, and this value (target lift amount) is obtained. Thus, the controller 17 controls the operation amount of the motor 15. The control shaft 11 is rotated by the operation of the motor 15, and the rotation position of the control arm 12 is controlled to an appropriate position between the large lift control position and the small lift control position.

  According to the control map of FIG. 7, the controller 17 determines that the lift amount increases at the higher rotation speed based on the target torque and rotation speed of the engine, and at the same engine rotation speed. If so, the rotational position of the control arm 12 is changed so that the lift amount increases as the target torque increases, that is, the lift amount increases as the load increases or increases. In other words, the controller 17 controls the lift variable mechanism VVL in accordance with the operating state of the engine as shown by the phantom line in FIG. 1 so that the intake valves 1 and 2 are relatively small on the low load or low rotation side. A lift control unit 17a is provided in the form of a program, which is a lift and a relatively large lift on the high rotation or high load side.

  In addition to the operation control of the variable lift mechanism VVL, in this embodiment, the lift phase angle of the intake valves 1 and 2 is changed according to the operating state of the engine by the operation control of the VCT 18. That is, VVL has a preferable characteristic that the phase angle is advanced as the lift amount is small as described above, and is retarded when the lift amount is large as described above. Since the rotation phase of the intake camshaft 3 is changed by the operation of the VCT 18 and the phase angle is advanced on the low load or low rotation side, the phase angle is retarded on the high load or high rotation side. is there.

  However, when the lift amount of the intake valves 1 and 2 is reduced in an operating range where the engine load and rotation speed are particularly low as in the case of an idle, if the phase angle is advanced accordingly, the intake valves 1 and 2 Is closed in the middle of the intake stroke of the cylinder, and the combustion stability may be impaired due to weakening of the flow in the cylinder. Therefore, at this time, the phase angle is retarded so that the intake valves 1 and 2 reach a lift peak in the middle of the intake stroke having the highest intake efficiency.

  That is, as shown in an example of the control map in FIG. 8, the controller 17 controls the VCT 18 according to the operating state of the engine and sets the maximum retard angle (advance amount 0 °) in the idling operation range. In most of the driving range, the phase angle is relatively advanced. In the example shown in the figure, the phase angle advances as the load increases from the idle operation range to the low / medium load range, and after reaching the maximum advance angle (60 ° adv), the phase increases as the load increases and the rotation speed increases. However, the maximum retard angle (advance amount 0 °) is reached again in a high load or high rotation range.

  The combination of such control of the phase angle by the VCT 18 and the above-described VVL operating characteristics results in the basic lift characteristics of the intake valves 1 and 2 as schematically shown in FIG. That is, as shown in the drawing, from the minimum lift curve L2 corresponding to the idling operation to the lift curve L3 intermediate between the minimum lift and the maximum lift, the intake valve 1, The closing timing of No. 2 has a so-called intake early closing characteristic on the advance side of the bottom dead center BDC of the cylinder.

  In such an operation range where the lift amount is relatively small, that is, in an operating range up to a medium load where the engine is operated frequently, the lift characteristics of the intake valves 1 and 2 are so-called early closing to further reduce cylinder pumping loss. Thus, the fuel consumption of the engine can be effectively reduced. In the intermediate lift curve L3, the opening period of the intake valves 1 and 2 is approximately the same as the intake stroke of the cylinder, and the intake valves 1 and 2 close at approximately the bottom dead center of the cylinder. The lift curve is such that the charging efficiency of intake air is roughly the highest in a low rotation range where the inertia of the engine is small.

  Further, on the lift side higher than the lift curve L3, the valve opening period is widened as the lift amount of the intake valves 1 and 2 increases, and the phase angle is retarded so that the closing timing of the intake valves 1 and 2 is increased. Is greatly retarded toward the maximum lift curve L1 with high load and high rotation. Thus, on the high-load high-rotation side where the output demand is high, the intake valves 1 and 2 are closed on the considerably retarded side with respect to the bottom dead center BDC, thereby effectively utilizing the inertia of the intake flow. The cylinder charging efficiency can be greatly increased.

  That is, as indicated by a virtual line in FIG. 1, the controller 17 controls the VCT 18 according to the operating state of the engine to advance and retard the lift phase angle of the intake valves 1 and 2. (Phase control means) are provided in the form of a program. As described above, the phase control unit 17b retards the phase angle so that the intake valves 1 and 2 are in the lift peak state in the middle of the intake stroke of the cylinder in the idle operation range, while at least on the high load side. In the adjacent partial load operation region, the phase angle is relatively advanced, and the VCT 18 is controlled so that the closing timing of the intake valves 1 and 2 is on the more advanced side than the BDC.

(Control at start-up)
Incidentally, as described above, the variable lift mechanism VVL includes the offset link 7, the connection link 8, the restriction link 13, and the like, and is configured to lift the intake valves 1 and 2 by the swing cams 4 and 5. Compared to a normal valve system, the structure is complicated and there are many mechanical sliding parts, so the frictional resistance to the operation tends to increase. In particular, when the direction of rotation of the swing cams 4 and 5 changes, the pressure distribution changes abruptly on the oil film of the sliding portion, so that the frictional resistance increases.

  Further, when cranking is started by a starter motor or the like at the start of the engine, an oil film is not sufficiently formed on many of the sliding portions of the variable lift mechanism VVL. The rotation resistance is considerably increased, and the rotational resistance against cranking is considerably increased due to the large number of sliding portions as described above.

  In this respect, if the lift amount of the intake valves 1 and 2 is set to, for example, the minimum lift utilizing the characteristics of the VVL, the compression reaction force of the valve spring 24 is reduced, so that the mechanism has many sliding portions as described above. However, the frictional resistance as a whole can be made equal to or rather smaller than that of a normal valve system. Therefore, it is conceivable to operate the motor 15 prior to cranking when the engine is started, for example, to achieve a minimum lift.

  FIG. 10 shows the experimental results of investigating the relationship between the lift amount of the intake valves 1 and 2 and the magnitude of the sliding frictional resistance in the valve operating system when the engine of this embodiment is operated at a low speed. According to the figure, as the lift amount of the intake valves 1 and 2 increases, the frictional resistance increases, and particularly when the lift amount is 3 mm or more, the frictional resistance increases rapidly as the engine speed decreases. It is shown. From this, it can be seen that the rotational resistance can be considerably reduced by reducing the lift of the intake valves 1 and 2 during cranking at about 250 to 300 rpm.

  However, if cranking is performed by lowering the lift of the intake valves 1 and 2 as described above, the rotational resistance can be reduced, but the amount of intake charge to the cylinder decreases as the lift amount decreases, and the effective compression ratio Will fall. Further, in this embodiment, as described above, as the characteristic of the variable lift mechanism VVL, as the lift amount of the intake valves 1 and 2 is decreased, the closing timing is advanced, so that the minimum lift is assumed. As shown in FIG. 6, the intake valves 1 and 2 are closed in the middle of the intake stroke, not only the intake charge amount is insufficient, but also the intake flow in the cylinder is weakened. It becomes difficult to promote vaporization and mixing with air.

  For this reason, when the engine is not warmed up and the engine is cold and the temperature around the cylinder and the intake system is low, the fuel cannot be sufficiently vaporized and mixed with the air. Combined with the decrease in the temperature and pressure in the cylinder near the dead center, the ignitability and combustibility of the air-fuel mixture are greatly reduced. As a result, the startability may not be secured.

  In view of this point, this embodiment pays attention to the fact that the rotational resistance is increased by one step particularly at the start of cranking as described above. When starting the engine, first, the lift amount of the intake valves 1 and 2 is minimized. Then, cranking is started with a small rotational resistance, and if a sufficient oil film is formed on each sliding portion of the VVL, the lift amount of the intake valves 1 and 2 is increased thereafter. Is.

  Hereinafter, a specific control procedure at the time of engine start by the controller 17 will be described based on the flowchart of FIG. 11 with a focus on the control of the variable lift mechanism VVL by the lift control unit 17a.

  The start control flow shown in the drawing starts when, for example, the ignition switch is turned on (IG on) in step S1, and in the subsequent step S2, the current lift amount of the variable lift mechanism VVL is detected. This can be detected from the rotation angle of the VVL motor 15, for example, or may be detected by a sensor or the like.

  Whether or not the current lift amount thus detected is a predetermined small lift state (in this example, the minimum lift is a 1 mm lift state shown in the lift curve L2 in FIG. 6, but is not limited to this). In the subsequent step S3, if it is a small lift state (YES), the process proceeds to step S5, while if it is not a small lift state (NO), the process proceeds to step S4 to the VVL motor 15 so as to enter the small lift state. After outputting the control signal, the process proceeds to step S5.

  In step S5, the engine water temperature is detected based on a signal from the water temperature sensor 26 (see FIG. 1), and in the subsequent step S6, it is determined whether or not the engine is not warmed up. This determination is made by determining whether or not the detected value of the engine water temperature is equal to or higher than a preset value (for example, it may be experimentally set between 60 to 80 ° C., hereinafter also referred to as a first set value). Is not warmed up below the first set value (determination is NO), the process proceeds to step S10 described later.

  On the other hand, if the engine water temperature is after warm-up of the first set value or more (determination is YES), the process proceeds to step S7, where the crankshaft is rotated by the starter motor and predetermined control such as fuel supply for each cylinder is performed ( Cranking with a small lift). Then, if the engine speed blows up to a predetermined value or more due to combustion of each cylinder of the engine in step S8 (complete explosion), the process proceeds to step S9 to shift to control for idling the engine (idling), and start control End (end).

  That is, first, by reducing the lift amount of the intake valves 1 and 2 at the start of cranking, even if the oil film is not sufficiently formed on each sliding portion of the variable lift mechanism VVL, its friction resistance Suppresses the increase of In addition, if the temperature around the cylinder or the intake system is high, such as during warm start, and the fuel is likely to vaporize, the effective compression ratio of the cylinder is low as a result of the small lift as described above. In addition, even if the in-cylinder flow is weak, the ignitability and combustibility of the air-fuel mixture can be secured. At this time, the intake valves 1 and 2 are kept in a small lift state until the engine reaches a complete explosion state, and the rotation resistance Is minimized so that the engine starts smoothly.

  On the other hand, in step S10, which is determined as YES when the engine is in an unwarmed state in step S6, it is determined whether or not the engine is in a low temperature state where the temperature is particularly low. That is, it is determined whether the detected value of the engine water temperature is lower than a second set value (for example, 10 ° C.) that is lower than the first set value for determining the unwarmed state, and the engine water temperature is the second set value. If it is less than the set value (determination is YES), the process proceeds to step S13, which will be described later. If the engine water temperature is equal to or higher than the second set value (determination is NO), the process proceeds to step S11, and cranking is started. Predetermined control such as fuel supply for each cylinder is performed.

  Subsequently, in step S12, for example, the lift amount of the intake valves 1 and 2 is increased in accordance with the rotation of the crankshaft of the engine by controlling the motor 15 of the variable lift mechanism VVL based on a signal from a crank angle sensor. (lift up). That is, for example, the minimum lift is maintained until the crankshaft rotates once, and then the lift amount is increased continuously (or intermittently) according to the progress of the crank angle so that the predetermined target value is reached during cranking. To be.

  Then, if the engine is in a complete explosion state and starts self-sustaining operation in the same manner as after the warm-up (S8), the process proceeds to step S9 and shifts to control for idling the engine (idling), and the start control is performed. End (end).

  Thus, if the engine is in an unwarmed state at the start, that is, during the so-called cold start, cranking is started while the lift amount of the intake valves 1 and 2 is minimized as in the warm start. If the engine oil reaches the sliding portion of the variable lift mechanism VVL and the frictional resistance decreases, then the lift amount is increased during cranking. At this time, since the hydraulic pressure supplied from the oil pump is insufficient when the engine is started and the operation of the VCT 18 is not stable, the phase angle of the lift of the intake valves 1 and 2 is not changed and is maintained at the maximum delay angle.

  Therefore, when the lift amount is increased during cranking as described above, the lift curves of the intake valves 1 and 2 change according to the characteristics of the variable lift mechanism VVL shown in FIG. Since the closing timing of the valves 1 and 2 approaches the bottom dead center BDC of the cylinder, the intake charge efficiency of the cylinder is effectively increased, the effective compression ratio is increased, and the intake flow in the cylinder is also enhanced. Fuel atomization and mixing with air is promoted. Therefore, even in an unwarmed state, it is possible to improve the ignitability and combustibility of the air-fuel mixture in the cylinder and to ensure good startability.

  Thus, the target value of the lift amount (start target lift amount) to be increased during cranking is read from, for example, a map shown in FIG. 12 according to the engine water temperature at start detected in step S5. This map is obtained by setting an optimum value of the lift amount experimentally obtained in advance in association with the engine water temperature at the time of starting. In the example of the figure, in an unwarmed state where the engine water temperature is less than the first set value. From the first set value to the second set value, the lift amount is set to increase as the temperature decreases.

  When the degree of increase in the lift amount of the intake valves 1 and 2 during cranking is changed according to the temperature state at the time of engine start in this way, the lift curves of the intake valves 1 and 2 during cranking are as shown by broken lines in FIG. The minimum lift curve L2 and the intermediate lift curve L4 change according to the engine water temperature at the time of starting, and the lower the temperature, the larger the lift, and the higher the temperature, the smaller the lift. That is, as the engine water temperature at the start is lower and the vaporization of fuel is worse, the lift amount of the intake valves 1 and 2 increases as shown by the solid line in FIG. The closing timing is retarded and approaches the bottom dead center of the cylinder, which can effectively increase the amount of intake air charged into the cylinder and enhance the in-cylinder flow.

  On the other hand, when the engine water temperature is not so low even during cold start, the lift amount of the intake valves 1 and 2 does not become so large as shown by the broken line in FIG. In this way, the lift amount of the intake valves 1 and 2 changes finely according to the temperature state of the engine at the time of starting, and the intake valve is only the minimum necessary to ensure the ignitability and combustibility of the air-fuel mixture during cranking. The lift amounts of 1 and 2 can be increased, whereby the increase in rotational resistance accompanying lift-up can be suppressed as much as possible, and the engine can be started more smoothly.

  According to the map shown in FIG. 12, if the engine water temperature is a low temperature state lower than the second set value, the target lift amount is constant regardless of the engine water temperature. The lift characteristic (lift curve L4 in FIG. 13) is such that the intake charge efficiency during ranking is the highest. On the other hand, the target lift amount when the engine water temperature at the start is equal to or higher than the first set value is 1 mm (minimum lift). This is because the lift amount of the intake valves 1 and 2 is cranking during the warm start described above. It corresponds to being kept at the minimum lift.

  Next, even at the cold start, particularly in a low temperature state where the temperature state is low, it is determined YES in Step S10, and the process proceeds to Step S13. Predetermined control such as fuel supply is performed. Subsequently, in step S14, the lift amount of the intake valves 1 and 2 is increased in accordance with the rotation of the crankshaft so that the lift amount suddenly increases in the middle thereof.

  That is, for example, as shown in FIG. 14 (b), the lift amount of the intake valves 1 and 2 is minimized until the crankshaft makes one rotation, and then relatively slowly with respect to the crank angle until the second rotation. The lift amount is increased, and the lift amount is rapidly increased at the third rotation to obtain a predetermined lift amount. This lift amount is a 5 mm lift in this example, but corresponds to a lift curve L4 shown in FIG. As shown in the figure, the lift curve L4 has a lift characteristic in which the intake valves 1 and 2 are closed at approximately the bottom dead center of the cylinder when the VCT 18 is at the maximum retarded angle, and the engine speed is low as at the start and flows into the cylinder. When the inertia of the intake air flow is small, the intake charge efficiency is roughly the highest.

  If the cranked engine is in a complete explosion state and starts a self-sustaining operation (S8), the process proceeds to step S9, shifts to control for idling the engine (idling), and the start control ends. (End).

  In this way, when the engine water temperature is particularly low, considering that the viscosity of the engine oil is high and it becomes difficult to form an oil film in the sliding portion of the VVL, the degree of increase in the lift amount is reduced for a while after the cranking is started, Thereafter, the degree of increase in the lift amount is increased. In this way, even when the engine temperature is particularly low, such as during cold start in a cold region, after the engine oil has sufficiently turned around the sliding portion of the lift variable mechanism VVL, The lift amount of 2 can be increased rapidly, and the intake charge amount to the cylinder can be increased in a short time, thereby improving the ignitability and combustibility of the air-fuel mixture while reducing cranking resistance and ensuring startability can do.

  In the control flow at the time of starting the engine shown in FIG. 11, steps S5, S6, and S10 constitute a temperature state determination unit 17c (determination means) that determines the temperature state of the engine based on a signal from the water temperature sensor 26. Yes. In other words, the controller 17 includes the temperature state determination unit 17c in the form of a program, as indicated by a virtual line in FIG.

  Steps S3, S4, S12, and S14 of the flow correspond to the control procedure of the lift control unit 17a when starting the engine. The lift control unit 17a first starts the intake valve 1 when starting the engine. , 2 are controlled so that a predetermined small lift state (minimum lift in this example) is closed during the intake stroke of the cylinder. Thereafter, if the engine is not warmed up, the intake valve 1 during cranking is controlled. , 2 is increased, and the VVL is controlled so that the lift amount is substantially constant if it is not warmed up.

  Further, the lift control unit 17a controls the VVL so that the degree of increase in the lift amount of the intake valves 1 and 2 increases as the temperature becomes lower in accordance with the engine water temperature at the time of starting. In the low state, the degree of increase in the lift amount of the intake valves 1 and 2 is increased during cranking.

  Therefore, according to the intake control device for an engine of this embodiment, the intake variable valves V1, 2 provided in the intake side valve system are controlled in accordance with the operating state (load and rotation speed) of the engine. By continuously changing the lift amount, it is possible to fill each cylinder with a necessary amount of air, so that the engine output can be controlled even if the throttle valve is eliminated. Therefore, the pumping loss can be reduced and the fuel consumption can be reduced.

  In addition, the VCT 18 that changes the rotational phase of the intake camshaft 3 controls the phase angle of the intake valves 1 and 2 according to the operating state of the engine. While further reducing fuel consumption as a closing characteristic, in the high-load high-rotation range where the lift amount increases, the intake flow inertia is maximized by delaying the closing timing of the intake valves 1 and 2 until after bottom dead center. The charging efficiency can be made sufficiently high by making effective use as much as possible, whereby a high engine output can be obtained.

  Furthermore, in the idle operation range, while the lift amount of the intake valves 1 and 2 is kept to a minimum, the phase angle is greatly retarded so that the lift peak is reached in the middle of the intake stroke of the cylinder with high intake efficiency. Even if the lift amount is small, the required charging efficiency can be obtained and the combustion stability can be ensured.

  As described above, as described above, when the engine is cold started, first, the lift amount of the intake valves 1 and 2 is minimized, and cranking is started with a small rotational resistance, whereby the lift is variable. Since the amount of lift can be increased after encouraging the formation of an oil film on the sliding part of the mechanism VVL, both reduction of cranking resistance and improvement of ignitability and combustibility of the air-fuel mixture are achieved in an appropriate balance. Thus, good startability can be ensured even in the cold.

  Moreover, the lift-up is the minimum necessary to ensure the ignitability and combustibility of the air-fuel mixture by finely changing the lift amount of the intake valves 1 and 2 to be increased during cranking according to the engine temperature at the start. The engine can be started more smoothly by minimizing the increase in rotational resistance associated therewith.

  In particular, when the engine temperature is low, after the cranking starts, the degree of increase in the lift amount is reduced for a while and then the degree of increase in the lift amount is increased, thereby reducing the cranking resistance and the cylinder even in cold regions. Both good ignitability and ensuring of combustibility can be achieved, and good startability can be obtained.

(Other embodiments)
The configuration of the present invention is not limited to the above-described embodiment, and includes other various configurations. That is, in the above embodiment, as shown in FIG. 14 (a), the lift amount of the intake valves 1 and 2 is minimized until the crankshaft makes one revolution at the time of cold start of the engine, and thereafter, according to the rotation of the crankshaft. However, the period for keeping the minimum lift is not necessarily limited to one rotation of the crankshaft.

  Further, in the low temperature state where the engine water temperature is particularly low as shown in FIG. 14B, the degree of increase in the lift amount of the intake valves 1 and 2 is changed during the cranking, but this is not essential. Even in a low temperature state, the lift amount may be increased substantially uniformly according to the rotation of the crankshaft as shown in FIG.

  Furthermore, the lift amount may be increased during cranking regardless of the temperature state of the engine at the start. For example, as shown in the flow of FIG. 15, after executing the same control procedure as that of steps S1 to S4 of the flow of FIG. 11 in steps T1 to T4, cranking is started in step T5, and in the subsequent step T6, FIG. As in step S12 of the flow, the lift amount of the intake valves 1 and 2 is increased according to the rotation of the crankshaft of the engine (lift up). Then, after the engine reaches a complete explosion state in steps T7 and T8, the control shifts to idle control, and the start control is terminated (end).

  In the flow of FIG. 15, steps T3, T4, and T6 correspond to the control procedure of the lift control unit 17a when the engine is started. Also in this case, it is preferable that the lift control unit 17a controls the VVL so that the degree of increase in the lift amount of the intake valves 1 and 2 increases as the temperature becomes lower, according to the engine water temperature at the start. .

  Further, the specific configuration of the variable lift mechanism VVL provided in the valve train of the engine is not limited to the above embodiment. For example, as shown in FIG. 16, the lift variable mechanism VVL does not change the lift peak timing even if the lift amount of the intake valves 1 and 2 changes, and the opening timing is advanced according to the increase in the lift amount. The closing time may be delayed.

  Even in that case, by controlling the VCT 18 in accordance with the operating state of the engine, the lift characteristics of the intake valves 1 and 2 are roughly outlined, and basically the phase angle advances on the low load or low rotation side as shown in FIG. The phase angle can be changed so that the phase angle is retarded on the high load or high rotation side, and the phase angle can be retarded during idling.

  Further, the VCT 18 may not be equipped, but in this case, the lift phase angle of the intake valves 1 and 2 cannot be changed independently. Therefore, in order to ensure idle stability, as shown in the figure. It is preferable to set the lift peak timing of the intake valves 1 and 2 roughly in the middle of the intake stroke of the cylinder.

  Also in the case of using VVL that changes the lift characteristics of the intake valves 1 and 2 as shown in FIG. 16, when the engine is cold started, first, the lift amount of the intake valves 1 and 2 is minimized (not shown). Lift curve L2), cranking is started with a small rotational resistance, and this promotes the formation of an oil film on the sliding part of the VVL. As shown by the arrow, for example, the lift amount of the intake valves 1 and 2 may be increased up to the lift curve L4.

  The present invention is an intake control device that continuously changes the lift amount of an intake valve in accordance with the operating state of an engine, and can effectively reduce fuel consumption on a low-load, low-rotation side that is frequently operated. In addition, since good startability can be ensured even during cold start such as in cold districts, high commerciality is required, and it is particularly useful for automobile engines that have a large change in use environment.

1 is a perspective view showing an embodiment in which an intake control device of the present invention is applied to an in-line four-cylinder engine. It is sectional drawing which shows the large lift control state of a lift variable mechanism, (a) shows the state of zero lift, (b) shows the state of a lift peak. FIG. 3 is a view corresponding to FIG. 2 showing a small lift control state. It is explanatory drawing of the action | operation of a large lift control state. FIG. 5 is a view corresponding to FIG. 4 related to a small lift control state. It is a characteristic view which shows the change of the lift curve by a lift variable mechanism. It is a figure which shows an example of the control map of lift amount. It is a figure which shows an example of the control map of a phase angle. It is explanatory drawing which shows the change of the lift curve during engine operation. It is a graph which shows the relationship between the lift amount of an intake valve, and sliding frictional resistance. It is a flowchart figure which shows control procedures, such as a lift amount at the time of starting. It is a map figure of the target lift amount at the time of starting. FIG. 10 is a view corresponding to FIG. 9 when the engine is started. It is an image figure which shows typically the change of the lift curve during cranking, (a) shows an unwarmed state, (b) shows a low-temperature state. FIG. 12 is a view corresponding to FIG. 11 according to another embodiment in which the lift amount of the intake valve is increased during cranking regardless of the engine temperature at the start. FIG. 14 is a view corresponding to FIG. 13 according to another embodiment in which the change characteristic of the lift curve by the variable lift mechanism is different.

Explanation of symbols

1, 2 Intake valve 3 Camshaft 4, 5 Oscillating cam (lift variable mechanism)
6 Eccentric cam (lift variable mechanism)
7 Offset link (lift variable mechanism)
8 Link (lift variable mechanism)
11 Control shaft (variable lift mechanism)
12 Control arm (lift variable mechanism)
13 Restriction link (lift variable mechanism)
17 Controller 17a Lift control unit (lift control means)
17b Phase control unit (phase control means)
17c Temperature state determination part (determination means)
18 Phase variable mechanism (VCT)

Claims (8)

There is provided a variable lift mechanism capable of continuously changing the lift amount of the intake valve lifted by the swing cam by changing the swing range of the swing cam. In the intake control device for the engine that is controlled based on
The lift variable mechanism changes its lift characteristic so that the valve opening period is extended with the increase of the lift amount of the intake valve so that the closing timing is delayed,
When the engine is started, first, a lift control means for controlling the variable lift mechanism is provided so that the intake valve enters a predetermined small lift state that is closed in the middle of the intake stroke of the cylinder, and the lift amount increases during the subsequent cranking. An intake control device for an engine, comprising: The intake control device according to claim 1,
The lift control means controls the variable lift mechanism so that the lift amount of the intake valve is minimized until the crankshaft rotates at least once, and then the intake valve closing timing is gradually increased according to the rotation of the crankshaft. An intake control device for an engine characterized by increasing the lift amount of the intake valve so as to approach the bottom dead center of the cylinder after being delayed. In the intake control device according to claim 1 or 2,
A determination means for determining the temperature state of the engine;
The lift control means controls the variable lift mechanism so that the degree of increase in the lift amount of the intake valve increases as the temperature decreases, according to the engine temperature state determined by the determination means. The intake control device for the engine. There is provided a variable lift mechanism capable of continuously changing the lift amount of the intake valve lifted by the swing cam by changing the swing range of the swing cam. In the intake control device for the engine that is controlled based on
The lift variable mechanism changes its lift characteristic so that the valve opening period is extended with the increase of the lift amount of the intake valve so that the closing timing is delayed,
Determination means for determining the temperature state of the engine;
When starting the engine, first, the variable lift mechanism is controlled so that the intake valve is in a predetermined small lift state that is closed in the middle of the intake stroke of the cylinder, and then the engine temperature state determined by the determination means is the predetermined temperature. The lift variable mechanism is set so that the lift amount of the intake valve increases during cranking if it is less than the unwarmed state, and so that the lift amount becomes substantially constant if it is not the unwarmed state. An engine intake control device comprising: lift control means for controlling. In the intake control device of claim 4,
The lift control means controls the variable lift mechanism so that the lift amount of the intake valve is minimized until the crankshaft rotates at least once, and thereafter, if the engine is in an unwarmed state, the crankshaft rotates. Accordingly, an intake control device for an engine is characterized by increasing the lift amount of the intake valve so that the closing timing of the intake valve is gradually retarded and approaches the bottom dead center of the cylinder. In the intake control device of claim 5,
The lift control means controls the variable lift mechanism so that the degree of increase in the lift amount of the intake valve increases as the temperature decreases, according to the engine temperature state determined by the determination means. Engine intake control device. In the intake control device according to claim 5 or 6,
An engine intake control device characterized in that the lift control means controls the variable lift mechanism so that the degree of increase in the lift amount of the intake valve increases and changes during cranking. In the intake control device according to any one of claims 4 to 7,
A variable phase mechanism capable of continuously changing the phase angle of the lift of the intake valve; and
When the engine is in the idle operating range, the intake valve is in a lift peak state in the middle of the intake stroke of the cylinder, and when it is in the partial load operating range adjacent to the high load side of the idle operating range, Phase control means for controlling the phase variable mechanism so that the phase angle is advanced, and
If the lift control means is not warmed up when the engine is started, the lift control means increases the lift amount of the intake valve until the closing timing of the intake valve is retarded from the idle operation. A featured engine intake control system.

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