JP4007350B2 - Control method of variable compression ratio mechanism - Google Patents

Description

  The present invention relates to a variable compression ratio mechanism that changes the compression ratio of an internal combustion engine, and more particularly to a suitable control method for the variable compression ratio mechanism.

In recent years, an internal combustion engine having a variable compression ratio mechanism for changing the compression ratio has been proposed. As the variable compression ratio mechanism, the cylinder block is configured to be slidable in the cylinder axial direction with respect to the crankcase, and the cylinder block and the crankcase are connected via an eccentric shaft to change the rotational position of the eccentric shaft. A mechanism for displacing the cylinder block by this is known (see, for example, Patent Document 1).
JP 2003-206791 A

  By the way, in the variable compression ratio mechanism, the load applied to the variable compression ratio mechanism varies depending on the operating position of the variable compression ratio mechanism and the operating state of the internal combustion engine. For example, in the conventional variable compression ratio mechanism described above, the load acting on the bearing of the eccentric shaft varies depending on the rotational position of the eccentric shaft and the combustion pressure of the internal combustion engine, so the friction coefficient between the eccentric shaft and the bearing varies.

  If the friction coefficient between the eccentric shaft and the bearing changes, a torque required for rotation of the eccentric shaft may be excessively increased, or a malfunction such as a failure of the eccentric shaft may be induced.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of appropriately operating the variable compression ratio mechanism without excessively increasing the drive torque of the variable compression ratio mechanism. It is to provide.

  The present invention employs the following means in order to solve the above-described problems. That is, a feature of the present invention is a method for controlling a variable compression ratio mechanism that involves a rotational sliding operation when changing the compression ratio of an internal combustion engine, wherein the lubrication state of the sliding portion of the variable compression ratio mechanism is a Stribeck line. In the fluid lubrication region in the figure, the rotational speed of the sliding portion is decreased, and when it is in the boundary lubrication region or the mixed lubrication region, the rotational speed of the sliding portion is increased.

  Stribeck diagram shows friction coefficient of sliding part: μ and lubrication characteristic value (= η · V / P, η: viscosity of lubricating oil, V: rotational speed of sliding part, P: acting on sliding part It is a characteristic view showing the relationship of load.

  In the boundary lubrication region and the mixed lubrication region of the Stribeck diagram, the friction coefficient: μ increases as the lubrication characteristic value: η · V / P decreases. That is, in the boundary lubrication region and the mixed lubrication region, the friction coefficient: μ decreases as the operation speed: V increases.

  In the fluid lubrication region of the Stribeck diagram, the smaller the lubrication characteristic value η · V / P, the smaller the friction coefficient μ. That is, in the fluid lubrication region, the friction coefficient: μ decreases as the operating speed: V decreases.

Accordingly, when the sliding portion is in the boundary lubrication region or the mixed lubrication region in the Stribeck diagram, when the sliding portion rotational speed V is increased, the sliding portion friction coefficient μ decreases. When the rotational speed V of the sliding portion is lowered when in the fluid lubrication region, the friction coefficient μ of the sliding portion decreases.

  As a result, the driving torque required for the rotation operation of the sliding portion is reduced, and the durability of the sliding portion is improved.

  When the rotational speed of the sliding portion is controlled, the rotational speed V may be controlled so that the friction coefficient μ of the sliding portion is a predetermined value or less. The predetermined value at that time is preferably a value at which the variable compression ratio mechanism can operate without a response delay when an appropriate driving torque is input to the variable movement mechanism.

  Thus, if the rotational speed V of the sliding portion is controlled so that the friction coefficient μ is equal to or less than a predetermined value, the variable compression ratio mechanism can be properly operated with a relatively small driving torque.

  Further, in the fluid lubrication region of the Stribeck diagram, the friction coefficient: μ increases as the load P acting on the sliding portion decreases, so that the rotational speed V decreases as the load P decreases. Good. On the other hand, in the boundary lubrication region and the mixed lubrication region of the Stribeck diagram, since the friction coefficient: μ increases as the load P acting on the sliding portion increases, the rotational speed V increases as the load P increases. You may do it.

  In the present invention, when the variable compression ratio mechanism is a mechanism that changes the relative position of the cylinder block with respect to the crankcase by changing the rotation angle of the eccentric cam shaft, the eccentric cam shaft is used as a parameter for the rotation angle of the eccentric cam shaft. The rotation speed may be determined.

  In the fluid lubrication region of the Stribeck diagram, the friction coefficient: μ of the bearing portion increases as the load: P decreases (the lubrication characteristic value: η · V / P increases). In contrast, if the rotational speed V of the eccentric cam shaft is lowered as the load P decreases, the lubrication characteristic value η · V / P also decreases accordingly. Therefore, the friction coefficient μ of the bearing portion is reduced. Is possible.

  In the boundary lubrication region or the mixed lubrication region of the Stribeck diagram, the friction coefficient: μ of the bearing portion increases as the load: P increases (the lubrication characteristic value: η · V / P decreases). On the other hand, if the rotational speed V of the eccentric cam shaft increases as the load P increases, the lubrication characteristic value η · V / P also increases accordingly, so the friction coefficient μ of the bearing portion is reduced. It is possible.

  Therefore, if the rotational speed V of the eccentric cam shaft is increased as the load P of the bearing portion increases, the friction coefficient μ of the bearing portion can be reduced.

  In the variable compression ratio mechanism that changes the relative position of the cylinder block with respect to the crankcase by changing the rotation angle of the eccentric cam shaft, the load P acting on the bearing portion of the eccentric cam shaft changes according to the compression ratio. For example, the load: P increases as the compression ratio increases, and the load: P decreases as the compression ratio decreases.

  Therefore, when the rotation angle of the eccentric cam shaft is at an angle that achieves a high compression ratio, the rotational speed of the eccentric cam shaft: V is higher than when the rotation angle is at an angle that achieves a low compression ratio. Coefficient of friction: μ can be reduced.

  Note that the load acting on the bearing portion of the eccentric cam shaft also varies depending on the combustion pressure of the internal combustion engine. For example, the load P of the bearing portion increases as the combustion pressure increases, and decreases as the combustion pressure decreases.

  Therefore, when the combustion pressure is high and the rotation angle of the eccentric cam shaft is at an angle that achieves a high compression ratio, the combustion pressure is low and the rotation angle of the eccentric cam shaft is at an angle that realizes a low compression ratio. If the rotational speed V of the eccentric cam shaft is increased, the friction coefficient μ of the bearing portion can be reduced.

  According to the control method of the variable compression ratio mechanism according to the present invention, since the friction coefficient of the sliding portion of the variable compression ratio mechanism can be reduced, the variable compression ratio mechanism can be varied without excessively increasing the drive torque. The compression ratio mechanism can be operated properly. Furthermore, the durability of the sliding portion is improved by reducing the friction coefficient.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 includes a cylinder block 2, a crankcase 3, and a cylinder head 4.

  The cylinder block 2 is attached to the crankcase 3 so as to be displaceable in the cylinder 20 axial direction. A connecting mechanism between the cylinder block 2 and the crankcase 3 is provided with a displacement mechanism 5 for displacing the cylinder block 2 and an actuator 50 for driving the displacement mechanism 5. The displacement mechanism 5 and the actuator 50 correspond to the variable compression ratio mechanism according to the present invention.

  FIG. 2 is a diagram illustrating the configuration of the displacement mechanism 5 and the actuator 50. A plurality of raised portions are formed at the lower portions on both sides of the cylinder block 2, and a cam housing hole 6 is formed in each raised portion. These cam housing holes 6 are formed in parallel to the cylinder arrangement direction and on the same axis.

  The crankcase 3 is formed with a standing wall portion so as to be positioned between the plurality of raised portions in which the above-described cam housing holes 6 are formed. A semicircular recess is formed on the surface of each standing wall portion facing the outside of the crankcase 3. A cap 7 having a semicircular recess is fixed to each standing wall by a bolt. When the standing wall portion and the cap 7 are fixed, a circular bearing housing hole 8 is formed by both concave portions. The inner diameter of the bearing accommodation hole 8 is the same as that of the cam accommodation hole 6.

  When the cylinder block 2 and the crankcase 3 configured as described above are connected, communication holes in which the cam storage holes 6 and the bearing storage holes 8 are alternately arranged are formed on both side surfaces of the cylinder block 2 and the crankcase 3. Is done. The eccentric cam shafts 5 are respectively inserted into these communication holes.

  Each eccentric cam shaft 5 includes a single shaft portion 5a, a plurality of cam portions 5b, and a movable bearing portion 5c. The cam portion 5b has a regular circular cam profile and is eccentrically fixed to the shaft portion 5a. The movable bearing portion 5c has the same shape as the cam portion 5b and is rotatably attached to the shaft portion 5a.

  The cam portions 5b and the movable bearing portions 5c are alternately arranged such that the cam portions 5b are accommodated in the cam housing holes 6 and the movable bearing portions 5c are accommodated in the bearing housing holes 8.

    An actuator 50 is provided at one end of the eccentric cam shaft 5 thus configured. The actuator 50 includes worm wheels 51a and 51b fixed to one end of the shaft portion 5a of each eccentric cam shaft 5, worms 52a and 52b meshing with the worm wheels 51a and 51b, and a motor 53 that rotationally drives the worms 52a and 52b. It has.

  The centers of the worm wheels 51a and 51b are offset from the center axis of the shaft portion 5a and coincide with the center of the cam portion 5b. Further, the spiral grooves of the worms 52a and 52b are formed in opposite directions, and the two eccentric cam shafts 5 are rotated in the opposite directions by the rotation of the motor 53.

  Returning to FIG. 1, the displacement mechanism 5 is provided with a rotation angle sensor 9 for detecting the rotation angle of the shaft portion 5a. The rotation angle sensor 9 is electrically connected to an electronic control unit (ECU) 100.

  The ECU 11 is an arithmetic logic operation circuit including a CPU, a ROM, a RAM, a backup RAM, and the like, and controls the motor 53 based on the output signal of the rotation angle sensor 9 and the operating state of the internal combustion engine 1.

  Here, a basic control method of the motor 53 will be described with reference to FIG. 3, a, b, and c represent the center of the shaft portion 5a, the center of the cam portion 5b, and the center of the movable bearing portion 5c, respectively.

  (A) in FIG. 3 shows a state where the compression ratio is the highest, in other words, a state where the cylinder block 2 is most displaced toward the bottom dead center side. In this case, the centers b and c of all the cam portions 5b and the movable bearing portions 5c are located on the same axis, and the outer peripheral surfaces of the cam portions 5b and the movable bearing portions 5c coincide in the axial direction. Correspondingly, the centers of the cam storage hole 6 and the bearing storage hole 8 also coincide with each other.

  When reducing the compression ratio from the state of FIG. 3A, the ECU 11 controls the motor 53 so that the two eccentric cam shafts 5 rotate in the direction of the arrow in the figure. FIG. 3B shows a state in which the eccentric cam shaft 5 is rotated approximately 45 ° from the state of FIG. In this case, the center b of the cam portion 5b is offset toward the top dead center side with respect to the center c of the movable bearing portion 5c, and accordingly the outer peripheral surface of the cam portion 5b is also top dead with respect to the outer peripheral surface of the movable bearing portion 5c. Offset to the point side.

  When the cam portion 5b is offset to the top dead center side with respect to the movable bearing portion 5c, the cam storage hole 6 is also offset to the top dead center side with respect to the bearing storage hole 8, so that the cylinder block 2 is connected to the crankcase 3. Is displaced toward the top dead center. As a result, the combustion chamber volume is increased, and the compression ratio of the internal combustion engine 1 is reduced.

  When the ECU 11 controls the motor 53 to further rotate the two eccentric cam shafts 5 in the direction of the arrow in the figure, the offset amount between the cam portion 5b and the movable bearing portion 5c further increases, and the compression ratio is further reduced accordingly. Become. FIG. 3C shows a state in which the eccentric cam shaft 5 is rotated 90 ° from the state of FIG.

  At this time, the center a of the shaft portion 5a, the center b of the cam portion 5b, and the center c of the movable bearing portion 5c are aligned in the cylinder axial direction, and the offset amount between the cam portion 5b and the movable bearing portion 5c is maximized. That is, when the eccentric cam shaft 5 rotates 90 ° from the state of FIG. 3A, the displacement amount to the top dead center side of the cylinder block 2 becomes the maximum. As a result, the compression ratio of the internal combustion engine 1 is the lowest.

  When the compression ratio is increased from the state of FIGS. 3B and 3C, the ECU 11 rotates the motor 53 in the reverse direction so that the two eccentric cam shafts 5 are in the direction opposite to the arrow direction in FIG. What is necessary is just to make it rotate.

  According to the displacement mechanism 5 and the actuator 50 as described above, the cylinder block 2 can be displaced in the cylinder axial direction, and the compression ratio of the internal combustion engine 1 can be freely changed accordingly.

  By the way, in order to appropriately change the compression ratio of the internal combustion engine 1, it is necessary to smoothly rotate the eccentric cam shaft 5. For this reason, in the displacement mechanism 5 as described above, lubricating oil is supplied to the cam housing hole 6 and the bearing housing hole 8 (hereinafter collectively referred to as a bearing portion) that function as bearings for the eccentric cam shaft 5.

  However, depending on the rotational angle of the eccentric cam shaft 5 and the operating state (combustion pressure) of the internal combustion engine 1, the lubrication state of the bearing portion becomes inappropriate, the driving power of the motor 53 increases excessively, or the eccentric cam shaft 5 rotates. Defects etc. may occur.

  Here, the Stribeck diagram of the bearing portion is shown in FIG. The vertical axis in FIG. 4 represents the friction coefficient of the bearing part: μ, and the horizontal axis represents the lubrication characteristic value of the bearing part.

  The lubrication characteristic value is represented by a function: η · V / P: a load acting on the bearing portion from the eccentric cam shaft 5: P, a viscosity of the lubricating oil: η, and a rotational speed of the eccentric cam shaft 5: V. This is a value corresponding to the film thickness.

  The Stribeck diagram is divided into a fluid lubrication region, a mixed lubrication region, and a boundary lubrication region according to the magnitude of the lubrication characteristic value: η · V / P (film thickness of the lubricating oil).

  The fluid lubrication region is a region where the lubrication characteristic value η · V / P is relatively large (the lubricating oil film thickness is relatively thick). In this fluid lubrication region, the friction coefficient: μ decreases as the lubrication characteristic value η · V / P decreases. In other words, in the fluid lubrication region, the friction coefficient: μ decreases as the load: P increases.

  The mixed lubrication region is a region where the lubrication characteristic value η · V / P is relatively small (the lubricating oil film thickness is relatively thin). In this mixed lubrication region, the friction coefficient μ increases rapidly as the lubrication characteristic value η · V / P decreases. In other words, in the mixed lubrication region, the friction coefficient: μ increases rapidly as the load: P increases.

  The boundary lubrication region is a region where the lubrication characteristic value η · V / P is very small (the film thickness of the lubricating oil is almost zero). In this region, the friction coefficient: μ is the maximum regardless of the lubrication characteristic value: η · V / P.

  According to such a Stribeck diagram, when the lubrication characteristic value η · V / P is in the mixed lubrication region, the driving torque of the motor 53 may become excessively large. When the lubrication characteristic value η · V / P is in the boundary lubrication region, the eccentric cam shaft 5 may be difficult to rotate.

  Therefore, in the present embodiment, the ECU 100 determines that the rotational speed of the eccentric cam shaft 5 is V, so that the lubrication characteristic value: η · V / P does not enter the boundary lubrication region and the friction coefficient: μ is equal to or less than a predetermined value. In other words, the rotational speed of the motor 53 is controlled.

Hereinafter, a specific method for controlling the rotation speed of the motor 53 will be described with reference to FIG. FIG. 5 is a flowchart showing a motor rotation speed control routine. This motor rotation speed control routine is a routine stored in advance in the ROM of the ECU 100, and is a routine that the ECU 100 repeatedly executes at predetermined time intervals.

  In the motor rotation speed control routine, the ECU 100 first detects the operating state of the internal combustion engine 1 in S101. Specifically, the ECU 100 inputs an accelerator opening, an engine speed, or a fuel injection amount.

  In S102, the ECU 100 calculates the target compression ratio: ε based on the operating state detected in S101. In this case, the target compression ratio: ε is expressed by the rotation angle of the eccentric cam shaft 5.

  In S103, the ECU 100 inputs the output signal of the rotation angle sensor 9 (current rotation angle of the eccentric cam shaft 5): θ.

  In S104, the ECU 100 uses the operating state of the internal combustion engine 1 detected in S101, the target compression ratio calculated in S102: ε, and the rotation angle of the eccentric cam shaft 5 input in S103: θ as parameters. The rotational speed Vm of the motor 53 when the eccentric cam shaft 5 is rotated from the rotational angle θ to the target compression ratio ε is determined.

  As described above with reference to FIG. 4, the friction coefficient μ of the bearing portion varies depending on the load P. The load P of the bearing portion is correlated with the combustion pressure of the internal combustion engine 1 and the rotation angle of the eccentric cam shaft 5.

  FIG. 6 is a view showing the relationship between the load acting on the bearing portion: P, the rotation angle of the eccentric cam shaft 5: θ, and the combustion pressure of the internal combustion engine 1. The rotational angle of the eccentric cam shaft 5 is 0 ° when the compression ratio is the lowest (that is, in the state shown in FIG. 3A), and the highest compression ratio (that is, the above-described state). The rotation angle in the state of FIG. 3C is 90 °.

  In FIG. 6, the load: P increases non-linearly as the rotation angle: θ of the eccentric cam shaft 5 increases. In particular, as the rotational angle θ of the eccentric cam shaft 5 approaches 90 °, the increasing rate of the load P increases. Furthermore, the load P increases as the combustion pressure of the internal combustion engine 1 increases.

  Therefore, the ECU 100 determines the rotation speed: Vm of the motor 53 when rotating the eccentric cam shaft 5 from the rotation angle: θ to the target compression ratio: ε according to the map shown in FIG.

  In the map of FIG. 7, the higher the combustion pressure and the larger the rotation angle: θ (the larger the bearing load: P), the higher the rotation speed: Vm of the motor 53, the lower the combustion pressure, and the rotation angle: θ. Is smaller (the bearing portion load: P is smaller), the rotational speed Vm of the motor 53 is lower.

  According to the map of FIG. 7, it is possible to reduce the friction coefficient μ of the bearing portion, regardless of the region of the Stribeck diagram where the bearing is lubricated.

  For example, in the fluid lubrication region of the Stribeck diagram, the friction coefficient: μ of the bearing portion increases as the load: P decreases (the lubrication characteristic value: η · V / P increases). The smaller the rotational speed V of the eccentric cam shaft 5 is, the smaller the lubrication characteristic value η · V / P is accordingly reduced, and the friction coefficient μ of the bearing portion is accordingly reduced.

Further, in the boundary lubrication region or mixed lubrication region of the Stribeck diagram, the friction coefficient: μ of the bearing portion increases as the load: P increases (the lubrication characteristic value: η · V / P decreases). If the rotational speed: V of the eccentric cam shaft 5 increases as the load: P increases, the lubrication characteristic value: η · V / P increases accordingly, and the friction coefficient of the bearing portion: μ decreases accordingly.

  Incidentally, the rotational speed Vm of the motor 53 shown in the map of FIG. 7 is the friction coefficient of the bearing portion μ, which is not more than a predetermined value (preferably about 0.1), and the lubrication characteristic value in the Stribeck diagram: η · V / P is determined so as to enter the fluid lubrication region as much as possible.

  Here, returning to FIG. 5, the ECU 100 controls the motor 53 in S105 according to the rotational speed Vm of the motor 53 determined in S104.

  According to the embodiment described above, the friction coefficient: μ of the bearing portion decreases and the film thickness of the lubricating oil becomes an appropriate thickness, so that the driving power of the motor 53 does not increase excessively and is eccentric. The durability of the camshaft 5 and the bearing portion is improved.

  According to the motor rotation control described above, since the rotation speed Vm of the motor 53 is lowered when the load P is relatively small, the time required for switching the compression ratio may be increased. In such a case, the extension of the required time may be suppressed by increasing the rotational speed Vm of the motor 53 in a region where the friction coefficient μ is sufficiently smaller than a predetermined value.

The figure which shows schematic structure of the internal combustion engine to which this invention is applied. Diagram showing configuration of displacement mechanism and actuator The figure explaining operation of a displacement mechanism Stribeck diagram showing the lubrication characteristics of the eccentric cam shaft bearing Flow chart showing motor rotation control routine The figure which shows the relationship between the load which acts on a bearing part, the rotation angle of an eccentric camshaft, and combustion pressure The figure which shows the control map of motor rotation speed

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 .... Internal combustion engine 2 .... Cylinder block 3 .... Crankcase 5 .... Displacement mechanism 6 .... Cam accommodation hole 8 .... Bearing accommodation hole 50 ... Actuator 500 ..Eccentric cam shaft

Claims (4)

A control method for a variable compression ratio mechanism that involves a rotational sliding operation when changing the compression ratio of an internal combustion engine,
When the lubrication state of the sliding portion of the variable compression ratio mechanism is in the fluid lubrication region in the Stribeck diagram, the rotational speed of the sliding portion is decreased, and when the sliding state is in the boundary lubrication region or the mixed lubrication region, the sliding A control method for a variable compression ratio mechanism, wherein the rotational speed of the part is increased.   2. The method of controlling a variable compression ratio mechanism according to claim 1, wherein the rotational speed of the sliding portion is controlled so that the friction coefficient of the sliding portion is a predetermined value or less. It is a control method of the variable compression ratio mechanism that changes the relative position of the cylinder block with respect to the crankcase by changing the rotation angle of the eccentric cam shaft,
A control method for a variable compression ratio mechanism, wherein the rotational speed of the eccentric cam shaft is increased or decreased using the rotation angle of the eccentric cam shaft as a parameter.   4. The method of controlling a variable compression ratio mechanism according to claim 3, wherein the rotational speed of the eccentric cam shaft is increased or decreased using the combustion pressure of the internal combustion engine as a parameter in addition to the rotational angle of the eccentric cam shaft.

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