JP4120465B2 - Internal combustion engine capable of changing compression ratio and compression ratio control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine capable of changing a compression ratio and a compression ratio control method thereof.
[0002]
[Prior art]
In recent years, various internal combustion engines (variable compression ratio engines) having a function capable of changing the compression ratio have been proposed. If the compression ratio is set high, power can be obtained efficiently, but knocking is likely to occur. For this reason, the compression ratio is changed according to the operating conditions. Specifically, when the load on the internal combustion engine is low, knocking is unlikely to occur and the compression ratio is set high. Thereby, fuel consumption improves. On the other hand, when the load on the internal combustion engine is high, knocking is likely to occur, so the compression ratio is set low.
[0003]
In changing the compression ratio in this way, a compression ratio changing mechanism has been proposed in which the crankcase that supports the crankshaft and the cylinder block on the piston head side are moved closer to and away from each other in the cylinder bore direction (for example, Patent Document 1). reference).
[0004]
[Patent Document 1]
JP 7-26981 A
[0005]
In Patent Document 1, an eccentric cam shaft is interposed between the engine members of the crankcase and the cylinder block, and a worm and a worm wheel are used for power transmission to the cam shaft. Then, the worm is connected to a drive source such as a motor, the worm wheel is connected to a drive target device (eccentric camshaft), the eccentric camshaft is rotated by forward / reverse rotation of the motor, and both the above engines follow the eccentric cam. The members are moved close to each other.
[0006]
[Problems to be solved by the invention]
In the above-described conventional variable compression ratio engine, the combustion pressure in the combustion chamber acts so that the relative position between the piston and the cylinder, that is, the crankcase and the cylinder block increases. Therefore, the force resulting from the combustion pressure acts as an auxiliary to the driving force required for the compression ratio changing mechanism when the compression ratio is changed from the high compression ratio to the low compression ratio.
[0007]
On the other hand, when the compression ratio is changed from the low compression ratio to the high compression ratio, the force resulting from the combustion pressure acts to hinder the driving of the compression ratio changing mechanism. In such a case, since it is necessary to drive the compression ratio changing mechanism against the combustion pressure, it is essential to transmit a large driving force to the compression ratio changing mechanism. By the way, in a situation where the engine load is high, the combustion pressure also increases in accordance with the engine load, and the force resulting from the combustion pressure also increases.Therefore, the compression ratio may be changed to the high compression ratio side in a high engine load situation. The driving force for transmission to the compression ratio changing mechanism is maximized. For this reason, in order to change the compression ratio uniformly in the upper and lower compression ratio range that can be changed by the compression ratio changing mechanism, the drive source has a high power characteristic that can exert the maximum driving force to be transmitted without any trouble. This necessitates an increase in the size of the engine including the mechanism for changing the compression ratio and the mechanism for changing the compression ratio.
[0008]
The present invention has been made to solve the above-described problems, and aims to reduce the size of equipment used for changing the compression ratio.
[0009]
[Means for solving the problems and their functions and effects]
In order to solve at least a part of such problems, in the internal combustion engine and the compression ratio control method thereof capable of changing the compression ratio according to the present invention, when the compression ratio is changed, the drive source is rotated for changing the compression ratio. The force is transmitted to the compression ratio changing mechanism as a transmission driving force through the transmission means. Thereby, the compression ratio changing mechanism drives at least one of the engine member on the piston head side and the engine member on the crankcase side to change the relative positional relationship between the two engine members, thereby changing the combustion chamber volume. The compression ratio is changed between a high compression ratio and a low compression ratio. In changing the compression ratio, a target compression ratio corresponding to the operation state of the internal combustion engine is obtained, and the compression ratio changing mechanism is driven by the power of the drive source so that the compression ratio becomes the target compression ratio.
[0010]
The present invention changes the compression ratio in this way, but does not change the compression ratio uniformly in the upper and lower compression ratio ranges that can be changed by the compression ratio changing mechanism. That is, when raising the compression ratio to the target compression ratio on the high compression ratio side, the following is performed. In such a situation, the force resulting from the combustion pressure of the fuel acts to inhibit the torque transmission of the rotational drive force of the drive source to the compression ratio changing mechanism via the transmission means. Therefore, the present invention limits the change of the compression ratio to the high compression ratio side according to the force resulting from this combustion pressure, and uses it as a drive source for driving the compression ratio changing mechanism to the high compression ratio side. This is intended to reduce the required torque.
[0011]
Therefore, according to the present invention, the drive source does not require high power characteristics, and the drive source can be downsized. Even with such a drive source, the compression ratio can be changed from the low compression ratio side up to the compression ratio (high compression ratio) limited as described above. The compression ratio can be changed between a compression ratio) and a lower limit compression ratio that can be changed by the compression ratio changing mechanism.
[0012]
On the other hand, if the force caused by the combustion pressure is reduced by reducing the load of the internal combustion engine, it is not necessary to limit the change of the compression ratio to the high compression ratio side, and the compression is performed against the force caused by the combustion pressure. The driving force of the driving source required for changing the ratio to the high compression ratio side is also reduced. Therefore, if the force due to the combustion pressure is reduced, the lower limit compression ratio and the upper limit compression ratio (or this upper limit) that can be changed by the compression ratio changing mechanism depending on the power characteristics even if the drive source is small. The compression ratio can be changed between high and low.
[0013]
In this way, the restriction on changing the compression ratio to the high compression ratio side according to the force caused by the combustion pressure is performed in a load region where the load of the internal combustion engine is higher than the normal load region that is frequently requested during operation of the internal combustion engine. Can be. In such a situation where the load is higher than the normal load region of the internal combustion engine, the force caused by the combustion pressure is also large, so the compression ratio change limitation as described above, and thus the torque reduction of the drive source function effectively, The drive source can be made more compact.
[0014]
In order to solve at least a part of such problems, in the internal combustion engine capable of changing another compression ratio of the present invention, the compression ratio is set to a high compression ratio in a load region higher than a normal load region that is frequently required for operation of the internal combustion engine. Under the condition of changing the compression ratio to the high compression ratio within the transmission torque range that the drive source can transmit to the compression ratio changing mechanism via the transmission means, The intermediate compression ratio is lower than the maximum compression ratio that can be changed by the compression ratio changing mechanism. In other words, instead of limiting the compression ratio change to the high compression ratio side according to the force caused by the combustion pressure, the compression ratio change to the high compression ratio side in the high load region is lower than the maximum compression ratio. The compression ratio is changed to the intermediate compression ratio. Even in this case, the drive source does not need power characteristics that can change the compression ratio up to the maximum compression ratio in a high load region, so that the drive source can be downsized.
[0015]
Thus, when changing the compression ratio to the intermediate compression ratio lower than the maximum compression ratio, the target compression ratio determined according to the operating state of the internal combustion engine is corrected to be reduced in the high load region where the load of the internal combustion engine is described above. do it. Alternatively, when the map for determining the target compression ratio according to the operating state of the internal combustion engine is changed to the high compression ratio side of the compression ratio in the high load region, the target compression ratio is changed to the intermediate compression ratio. In this manner, the target compression ratio at the time of changing the compression ratio in the high load region to the high compression ratio side can be determined as the intermediate compression ratio in the map after the change.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Next, the form of this invention is demonstrated based on an Example. FIG. 1 is a schematic exploded perspective view of a variable compression ratio engine 100 according to the first embodiment, and FIG. 2 is a schematic perspective view showing a schematic configuration of the variable compression ratio engine 100.
[0017]
The variable compression ratio engine 100 of the present embodiment changes the compression chamber by changing the combustion chamber volume by moving the cylinder block 103 relative to the lower case (crankcase) 104 in the axial direction of the cylinder 102. Therefore, the variable compression ratio engine 100 according to the present embodiment includes a compression ratio changing mechanism that moves the cylinder block 103 with respect to the lower case 104. This compression ratio changing mechanism will be described later.
[0018]
Since the cylinder block 103 moves in the axial direction of the cylinder 102 with respect to the lower case 104, the cylinder block 103 moves with respect to the lower case 104 even on a camshaft (not shown) that opens and closes an intake / exhaust valve disposed on the cylinder 102. It becomes. Since the driving force of the camshaft is transmitted from the crankshaft 115 disposed in the lower case 104 via a chain or belt, this is also taken into consideration in the engine of this embodiment. Since such a configuration is not directly related to the gist of the present invention, the description thereof is omitted.
[0019]
Regarding parts other than that the cylinder block 103 is movable with respect to the lower case 104 and that the moving mechanism (compression ratio changing mechanism) is provided, and that the fluctuating force is transmitted to the camshaft. There is no difference from a normal engine. Therefore, description of these is also omitted.
[0020]
As shown in FIG. 1, the variable compression ratio engine 100 includes a plurality of raised portions 130 at the lower portions on both sides of the cylinder block 103, and each raised portion 130 has a cam housing hole 105. The cam housing hole 105 has a circular shape, and is perpendicular to the axial direction of the cylinder 102 and parallel to the arrangement direction of the plurality of cylinders 102 (the variable compression ratio engine 100 of this embodiment is a four-cylinder engine). Each is formed to be. The cam storage holes 105 are formed on both sides of the cylinder block 103, and the plurality of cam storage holes 105 on one side are all located on the same axis. The pair of axes of the cam storage holes 105 on both sides of the cylinder block 103 are parallel.
[0021]
In the lower case 104, a standing wall portion 132 is formed so as to be positioned between the plurality of raised portions 130 in which the cam housing holes 105 are formed. A semicircular recess is formed on the surface of each standing wall 132 facing the outer side of the lower case 104. Each standing wall 132 is provided with a cap 107 to be attached by a bolt 106, and the cap 107 has a semicircular recess. When the cap 107 is attached to each standing wall portion 132, the circular bearing housing hole 108 is formed by both members. The shape of the bearing accommodation hole 108 is the same as that of the cam accommodation hole 105 described above.
[0022]
Similar to the cam housing hole 105, the plurality of bearing housing holes 108 are perpendicular to the axial direction of the cylinder 102 and parallel to the arrangement direction of the plurality of cylinders 102 when the cylinder block 103 is attached to the lower case 104. Become. The plurality of bearing housing holes 108 are also formed on both sides of the cylinder block 103, and the plurality of bearing housing holes 108 on one side are all located on the same axis. The pair of axes of the bearing housing holes 108 on both sides of the cylinder block 103 are parallel. The distance between the cam housing holes 105 on both sides and the distance between the bearing housing holes 108 on both sides are the same.
[0023]
Cam shafts 109 are respectively inserted into the two rows of cam storage holes 105 and bearing storage holes 108 that are alternately arranged. As shown in FIG. 1, the cam shaft 109 includes a cam portion 109b and a movable bearing portion 109c on a shaft portion 109a. The cam portion 109b is fixed to the shaft portion 109a while being eccentric with respect to the central axis of the shaft portion 109a, and has a regular circular cam profile. The movable bearing portion 109c has the same outer shape as the cam portion 109b and is rotatably attached to the shaft portion 109a. In the present embodiment, the cam portions 109b and the movable bearing portions 109c are alternately arranged. The pair of cam shafts 109 have a mirror image relationship with the cylinder 102 interposed therebetween. A mounting portion 109d of a worm wheel 110, which will be described later, is formed at the end of the cam shaft 109. The center axis of the shaft portion 109a and the center of the mounting portion 109d are eccentric, and the center of all the cam portions 109b and the center of the mounting portion 109d coincide.
[0024]
The movable bearing portion 109c is also eccentric with respect to the shaft portion 109a, and the amount of eccentricity is the same as that of the cam portion 109b. In order to actually construct the camshaft 109, the camshaft 109 is manufactured in a state in which one end of the cam portion 109b is integrally connected in advance, and the movable bearing portion 109c, the other cam portion 109b, Are inserted alternately. Only the cam portion 109b is fixed to the shaft portion 109a with a screw or the like as shown. In this case, the cam portion may be fixed by other methods such as press-fitting or welding. The number of cam portions 109b on the shaft portion 109a matches the number of cam housing holes 105 on one side of the cylinder block 103. Further, the thickness of the cam portion 109b also matches the length of each corresponding cam storage hole 105. Similarly, the number of movable bearing portions 109c on the shaft portion 109a matches the number of bearing housing holes 108 formed on one side of the lower case 104. Further, the thickness of the movable bearing portion 109c also matches the length of the corresponding bearing housing hole 108.
[0025]
In each cam shaft 109, the eccentric directions of the plurality of cam portions 109b are the same. In addition, since the outer shape of the movable bearing portion 109c is the same circle as the cam portion 109b, the outer surface of the plurality of cam portions 109b and the outer surface of the plurality of movable bearing portions 109c are rotated by rotating the movable bearing portion 109c. Can be matched. In this state, the cylinder block 103 and the lower case 104 are combined, and the cam shaft 109 is inserted into a long hole formed by the plurality of cam housing holes 105 and the plurality of bearing housing holes 108 and assembled. The cap 107 may be attached after the camshaft 109 is disposed with respect to the cylinder block 103 and the lower case 104.
[0026]
The cam housing hole 105, the bearing housing hole 108, the cam portion 109b, and the movable bearing portion 109c have the same exact circular shape. The cylinder block 103 is slidable with respect to the lower case 104, but a member such as a piston ring that secures the airtightness between the cylinder inner surface and the piston is arranged on the sliding surface of both of them so as to be airtight. Secure. Note that the sealing may be performed by a method other than the piston ring, for example, a rubber gasket such as an O-ring.
[0027]
Each camshaft 109 has a worm wheel 110 at an attachment portion 109d at the end of the shaft portion 109a. The worm wheel 110 is positioned with a key and is bolted to the mounting portion 109d.
[0028]
Worms 111a and 111b mesh with each worm wheel 110 corresponding to the pair of cam shafts 109. The worms 111a and 111b are connected to the output shaft of a single servo motor 112 that can rotate forward and backward. The worms 111a and 111b have a butterfly groove that rotates in opposite directions. For this reason, when the servo motor 112 is rotated, the pair of cam shafts 109 receives the rotation of the worm wheel 110 and rotates in opposite directions. The servo motor 112 is fixed to the cylinder block 103 or the like and moves integrally with the cylinder block 103.
[0029]
Next, how the compression ratio is changed in the variable compression ratio engine 100 of this embodiment will be described. FIG. 3 is an explanatory diagram for explaining how the device is driven when the compression ratio is changed in the variable compression ratio engine 100. FIGS. 3A to 3C are cross-sectional views showing a compression ratio changing mechanism including the cylinder block 103, the lower case 104, and the cam shaft 109 and the like constructed between them. In these drawings, the central axis of the shaft portion 109a of the cam shaft 109 is denoted by A, the center of the cam portion 109b is denoted by B, and the center of the movable bearing portion 109c is denoted by C.
[0030]
FIG. 3A shows a state in which the outer circumferences of all the cam portions 109b and the movable bearing portions 109c coincide with each other when viewed from the extension line of the shaft portion 109a. At this time, the pair of left and right shaft portions 109a are located outside the cam housing hole 105 and the bearing housing hole 108 here. The camshaft angle is defined as zero degrees (0 °) when each shaft portion has such a positional relationship.
[0031]
When the shaft portion 109a (and the cam portion 109b fixed to the shaft portion 109a) rotates in the direction of the arrow X + in the drawing from the state of FIG. 3A, the state of FIG. 3B is obtained. At this time, since the cam portion 109b and the movable bearing portion 109c are displaced in the eccentric direction with respect to the shaft portion 109a, the cylinder block 103 can be slid toward the top dead center side with respect to the lower case 104. The sliding amount becomes the maximum when the cam shaft 109 is rotated in the rotation direction indicated by the arrow X + until the state as shown in FIG. 3C is reached, and the amount of eccentricity of the cam portion 109b and the movable bearing portion 109c is two. Doubled. The cam portion 109b and the movable bearing portion 109c rotate inside the cam housing hole 105 and the bearing housing hole 108, respectively, and allow the position of the shaft portion 109a to move inside the cam housing hole 105 and the bearing housing hole 108, respectively. is doing.
[0032]
As is clear from FIGS. 3A and 3B, in FIG. 3A, since the relative distance between the cylinder block 103 and the lower case 104, and thus the piston top dead center position, is shortened, the combustion chamber volume is reduced and compression is performed. The ratio is high. On the other hand, as the cylinder block 103 moves away from the piston top dead center position as shown in FIG. 3C, the combustion chamber volume increases and the compression ratio becomes lower. That is, when the cylinder block 103 is driven from FIG. 3A to FIG. 3C, the compression ratio changes from the high compression ratio to the low compression ratio.
[0033]
The rotation direction of the camshaft 109 when the compression ratio transitions to the low compression ratio side is the arrow X + direction in FIG. 3, and at this time, the servomotor 112 is assumed to rotate forward. Further, the positional relationship between the shaft portions shown in FIG. 3C is assumed to be a cam shaft angle + 90 °.
[0034]
The cylinder block 103 receives the rotational driving force of the servo motor 112 upward through this cam shaft and moves upward away from the lower case 104. At this time, the force resulting from the combustion pressure in the combustion chamber acts in a direction to raise the cylinder block 103 from the lower case 104. Therefore, in the case of the compression ratio transition to the low compression ratio side, the combustion pressure is It works in the same direction as the driving force received by the cylinder block 103. In this case, since the rotation of each shaft part and the sliding movement of the cylinder block 103 occur, a frictional force accompanying such movement of the member also occurs, and this frictional force is driven by the motor driving via the camshaft, that is, the camshaft. Acts to inhibit force transmission.
[0035]
In a state where the cam portion 109b and the movable bearing portion 109c are completely aligned (FIG. 3A), the plurality of movable bearing portions 109c attached to one cam shaft 109 slide the cylinder up and down. There is also a possibility that it will run idle. For this reason, the engine compression ratio changing mechanism of the present embodiment does not cause a state in which the cam portion 109b and the movable bearing portion 109c are completely matched as shown in FIG. For example, when the rotation position of the cam shaft 109 in the state of FIG. 3A is set to 0 ° as a reference (the forward direction is the reverse rotation direction with the pair of cam shafts 109), the rotation position in the state of FIG. Although it is 90 ° in the positive direction along X +, camshaft rotation is realized in the range of 5 ° to 90 ° without using the vicinity of 0 ° (for example, about 5 °) shown in FIG. By doing so, the above-described problems can be solved. Since the actual slide amount of the cylinder block 103 is considered to be several mm, the eccentricity of the cam portion 109b and the movable bearing portion 109c is obtained so that a specified compression ratio range is obtained in the range of 5 ° to 90 °. It is sufficient to determine the amount, and there is no problem in actual design.
[0036]
In order to increase the compression ratio by returning the slide amount of the cylinder block 103 from the state of FIG. 3C to the original state, the servo motor 112 is rotated in the reverse direction. In this way, the shaft portion 109a, the cam portion 109b, and the movable bearing portion 109c of the cam shaft 109 are driven to rotate in the direction of the arrow X− in the drawing. Thereby, the cylinder block 103 returns to the state of FIG. 3A, and the compression ratio changes from the high compression ratio to the low compression ratio. The control range of the forward and reverse cam shaft 109 is a cam shaft angle of 5 ° to 90 ° as described above.
[0037]
When the compression ratio transition from the high compression ratio to the low compression ratio in the state of FIG. 3A occurs, the cylinder block 103 receives the rotational driving force of the servo motor 112 downward through the cam shaft, and the lower case. Descent toward 104. Even in this case, the combustion pressure in the combustion chamber works in a direction to raise the cylinder block 103 from the lower case 104. Therefore, when the compression ratio transitions to the high compression ratio side, the cylinder block 103 Then, it is driven toward the lower case 104 against the combustion pressure.
[0038]
The cylinder block 103 may be slid toward the bottom dead center side with respect to the lower case 104. In this case, the control range of the cam shaft 109 may be a cam shaft angle of −5 ° to −90 ° (355 ° to 270 °). Further, when the cylinder block 103 is slid to the top dead center side with respect to the lower case 104, the control range of the cam shaft 109 may be 90 ° to 175 ° or the like.
[0039]
By using the compression ratio changing mechanism as described above, the cylinder block 103 can be slid in the axial direction of the cylinder 102 with respect to the lower case 104. As a result, the compression ratio can be variably controlled.
[0040]
Next, an electrical configuration for changing and controlling the compression ratio of the variable compression ratio engine 100 will be described. FIG. 4 is a block diagram schematically illustrating a device configuration involved in the compression ratio change control of the variable compression ratio engine 100.
[0041]
As shown in the figure, the variable compression ratio engine 100 includes an ECU 160 that controls the compression ratio change, the driving of a throttle valve (not shown), and the like. The ECU 160 is configured as a logical operation circuit centered on a microcomputer, and includes an unillustrated actuator for driving a throttle valve, a throttle sensor 161, an accelerator sensor 162, and an engine speed and a crank angle for detecting an engine speed and a crank angle. The sensor 163 is connected to a servo motor 112 for changing the compression ratio, a motor rotation angle sensor 164 for detecting the rotation angle, and the like. ECU 160 calculates the actual rotation angle position of servo motor 112 based on the sensor output from motor rotation angle sensor 164, and calculates the actual compression ratio ε of the engine from the calculated position. In calculating the compression ratio, the motor rotation angle sensor 164 can be replaced with the following configuration. In other words, an electromagnetic clearance sensor can be incorporated in the combustion chamber of the cylinder, and the actual compression ratio can be calculated from the sensor output of the piston position in the combustion chamber.
[0042]
Next, the state of the compression ratio change in the variable compression ratio engine 100 having the above-described configuration and the relationship between the forces acting on the cylinder block 103 and the lower case 104 during the compression ratio transition will be described. FIG. 5 is an explanatory diagram showing the relationship between various torques involved in changing the compression ratio under a situation where the load required for the engine (engine load) is high.
[0043]
When each of the cam shaft portions described above is rotated over a cam shaft angle of 0 to 90 ° and the compression ratio is changed between the lower limit compression ratio εL and the upper limit compression ratio εM, the rotational drive of each cam shaft portion and the cylinder block 103 are changed. Because of this sliding movement, frictional force accompanying such movement of the member is generated. Also, a force due to the combustion pressure is generated. The force resulting from such frictional force and combustion pressure is determined in accordance with the cam shaft rotation angle (that is, compression ratio) of each cam shaft portion, and these forces are cylinders that have undergone rotation of each cam shaft portion. It is involved in driving torque transmission to the block 103. That is, the frictional force is a force that hinders the rotational drive of the cam shaft portion and the sliding movement of the cylinder block 103, and thus hinders the transmission of torque for causing such a member movement. For this reason, the servo motor 112 is required to have a torque against the frictional force accompanying such movement of the member, and this state is shown as a positive torque in FIG. As described above, the force caused by the combustion pressure works in a direction to raise the cylinder block 103 from the lower case 104. Therefore, when the compression ratio transitions to the low compression ratio side, It is advantageous for torque transmission through the. The state in which the force resulting from the combustion pressure is involved in the torque transmission is opposite to that in the case of the frictional force, and is shown as a negative torque in FIG.
[0044]
Consider a situation where the compression ratio is lowered from the upper limit compression ratio εM side to the lower limit compression ratio εL side when the engine load is high. In such a situation, on the high compression ratio side, the torque related to the force due to the combustion pressure is superior to the torque to resist the frictional force, and the direction is also consistent with the change side to the low compression ratio. Therefore, it is sufficient to transmit the rotational driving force of the servo motor 112 to the cylinder block 103 with the assistance of the force caused by the combustion pressure, and the servo motor 112 is adjusted to the torque curve in which the force caused by the combustion pressure is involved. What is necessary is just to generate a torque.
[0045]
When the compression ratio is changed from the lower limit compression ratio ε side to the upper limit compression ratio εM side, torque for resisting the frictional force and the force caused by the combustion pressure is required. It is necessary to generate a torque that combines a torque curve that involves a force caused by pressure and a torque that resists the frictional force.
[0046]
That is, in order to change the compression ratio between the lower limit compression ratio ε and the upper limit compression ratio εM under a situation where the engine load is high, the torque characteristic as shown in FIG. It is necessary to employ a servo motor 112 that can exhibit both the torque characteristics of the change and the change to the high compression ratio side) by forward and reverse rotation. By the way, since the change to the high compression ratio side needs to resist the force caused by the frictional force and the combustion pressure as described above, the servo motor 112 has a torque characteristic toward the high compression ratio side. In order to be able to do so, the ability (power characteristics) to exert the maximum negative torque (T-max) shown in the figure is required.
[0047]
If such a servo motor 112 is used, the maximum torque (T + max) can be obtained even on the + side, and the compression ratio can be changed between the lower limit compression ratio ε and the upper limit compression ratio εM under a situation where the engine load is high. Such torque characteristics are obtained by uniformly changing the compression ratio in the upper and lower compression ratio ranges that can be changed by sliding movement of the cylinder block 103 (rotation of the cam shaft portion). As a result, the motor has not been downsized. However, in this embodiment, the motor can be reduced in size by the compression ratio change restriction control described below.
[0048]
Here, the control content for changing the compression ratio in the variable compression ratio engine 100 of the present embodiment will be described. FIG. 6 is a flowchart showing the compression ratio change control, and FIG. 7 is an explanatory diagram for explaining the contents of the compression ratio control.
[0049]
The compression ratio change control routine shown in FIG. 6 is repeatedly executed at predetermined time intervals. First, an accelerator sensor 162 that reads the engine speed from the speed / crank angle sensor 163 and outputs an accelerator depression state, and a throttle The engine load (torque) is read according to the sensor output from the sensor 161 or an intake pipe negative pressure sensor (not shown) (step S100). Subsequently, a target compression ratio εt is calculated based on the read rotation speed / torque and the map shown in FIG. 7 in which both are associated with the compression ratio (step S110). A plurality of maps for calculating the target compression ratio are prepared depending on the engine cooling water temperature, the intake air temperature, the emission, or the like, and can be switched as appropriate according to the engine operating condition at that time.
[0050]
Next, the current rotation angle position of the servo motor 112 is read from the motor rotation angle sensor 164, and the current compression ratio is calculated based on this position (step S120). Next, it is determined whether or not the compression ratio needs to be changed based on the coincidence state between the calculated compression ratio εi and the target compression ratio εt (step S130). Here, if the above two compression ratios do not match, it is determined that the compression ratio needs to be changed, and the ECU 160 performs change control for setting the compression ratio to the target compression ratio εt (step S140). Repeat the process. The control in step S140 controls the servo motor 112 as described below. However, the motor drive is limited by the below-described limit control, and the change of the compression ratio is also limited accordingly. This point will be described later.
[0051]
In step 140, a drive signal having the number of pulses necessary for setting the current compression ratio εi to the target compression ratio εt is output to the servo motor 112 including the rotation direction. In other words, when changing from the current compression ratio to the low compression ratio side, the ECU 160 causes the servo shaft so that the shaft portion 109a, the cam portion 109b, and the movable bearing portion 109c of the cam shaft 109 are rotationally driven in the direction of the arrow X + in FIG. The rotation direction of the motor 112 is determined, and a drive signal having the number of pulses required for changing the compression ratio is output. The ECU 160 performs feedback control of the servo motor 112 in consideration of the number of pulses output and the number of pulses from the motor rotation angle sensor 164 when performing such rotation control of the servo motor 112.
[0052]
On the other hand, when changing to the high compression ratio side, the ECU 160 causes the servo motor 112 to rotate the shaft portion 109a, the cam portion 109b, and the movable bearing portion 109c of the cam shaft 109 in the direction of the arrow X− in FIG. , And a drive signal having the number of pulses required for changing the compression ratio is output. In this case, the ECU 160 performs rotation control (feedback control) of the servo motor 112 in the opposite direction to the case of the compression ratio transition to the low compression ratio side. By such control, the variable compression ratio engine 100 moves the cylinder block 103 up and down as described above by the compression ratio changing mechanism using the servo motor 112 as a drive source, thereby changing the compression ratio of the engine to high or low.
[0053]
In this embodiment, in parallel with the compression ratio change control to the target compression ratio as described above, the following restriction control for changing the compression ratio is also executed. FIG. 8 is a flowchart showing the contents of control for limiting the compression ratio change.
[0054]
The restriction control for changing the compression ratio shown in FIG. 8 is repeatedly executed every predetermined time while taking the execution timing with the compression ratio changing control shown in FIG. 6. First, the current situation is changed to the high compression ratio side. It is determined whether or not (step S200). This determination is made by comparing the target compression ratio εt described in FIG. 6 with the current compression ratio εi. Alternatively, the processing in steps S100 to S120 in FIG. 6 can be performed to determine whether or not the state is changed to the high compression ratio side.
[0055]
If a negative determination is made in step S200, the compression ratio is changed to the low compression ratio. In this case, the motor control for changing the compression ratio in step S140 described above is continued (step S140). S210). As a result, the ECU 160 changes the current compression ratio εi to a lower target compression ratio εt after outputting a drive signal having the number of pulses necessary to set the current compression ratio εi to the target compression ratio εt (step S140). reference). That is, the compression ratio is changed to the target compression ratio εt lower than the current compression ratio εi without any limitation as long as it is changed to the low compression ratio side.
[0056]
On the other hand, if it is determined positive in step S200 that the change is to the high compression ratio side, the current combustion pressure P is read (step S220), and whether or not the combustion pressure P is equal to or higher than the specified combustion pressure P0. Is determined (step S230). In this case, the combustion pressure P is obtained from an output from a sensor (not shown) that detects the internal pressure in the engine cylinder, and the engine speed read from the rotation speed / crank angle sensor 163 and the intake pipe negative pressure from a sensor (not shown). The combustion pressure P can be estimated from a map (not shown) based on the throttle opening from the throttle sensor 161 and the like.
[0057]
If the combustion pressure P is lower than the specified combustion pressure P0, a negative determination is made in step S230, the process proceeds to step S210 described above, and motor control for changing the compression ratio is continuously executed. Since the negative determination in step S230 is subsequent to the determination of changing to the high compression ratio in step S200, the compression ratio change in this case is performed to a target compression ratio εt higher than the current compression ratio εi. However, since the combustion pressure P is not so high, it is executed without restriction.
[0058]
However, if it is determined in step S230 that the combustion pressure P is equal to or higher than the specified combustion pressure P0, the motor control for changing the compression ratio in step S140 described above is temporarily stopped (step S240). The ECU 160 performs motor control based on step S140 so as to change the current compression ratio εi to a higher target compression ratio εt. In the course of the control, the ECU 160 temporarily stops the motor control. Therefore, under a situation where the combustion pressure P is high, the change of the compression ratio to the high compression ratio side is limited, and the compression ratio is changed to the high compression ratio side only up to the compression ratio determined when the motor control is temporarily stopped. Will not be.
[0059]
The above-described restriction of the compression ratio change will be described with reference to the drawings. FIG. 9 is an explanatory diagram for explaining the change in the compression ratio when the change in the compression ratio is restricted while showing the torque relationship in FIG. 5 when the engine load is high.
[0060]
Now, the current compression ratio εi is the lower limit compression ratio εL that can be changed by the sliding movement of the cylinder block 103, or the compression ratio εL1 in the vicinity thereof, and the target compression ratio εt is the upper limit compression ratio εM in step S110 of FIG. It is assumed that the compression ratio is in the vicinity. Thus, in the situation where the current compression ratio is low and this is changed to the high compression ratio, the combustion pressure P is not so high because the compression ratio is low although the engine load is high, and negative in step S230 of FIG. Determined. Therefore, the compression ratio is not limited in step S240, and as shown along the torque diagram (high compression side torque diagram) for changing the compression ratio toward the high compression ratio, εL2, εL3,. It is changed to the high compression ratio side.
[0061]
However, when the compression ratio is changed to the high compression ratio up to the compression ratio εLm in the figure, the combustion pressure P also increases due to such an increase in the compression ratio, and a positive determination is made in step S230. Accordingly, since the motor drive for changing the compression ratio is temporarily stopped at this time (step S240), the change of the compression ratio toward the higher compression ratio is limited, and the compression ratio is only high up to the compression ratio εLm. Don't be. That is, although the target compression ratio εt is higher than the compression ratio εLm, the actual compression ratio is limited to a compression ratio εLm lower than the target compression ratio εt.
[0062]
When the change of the compression ratio toward the high compression ratio is thus limited, the servo motor 112 only needs to exhibit torque characteristics for changing the compression ratio from the low compression ratio side to the compression ratio εLm. In this case, the negative maximum torque (TL-max) is smaller than the maximum torque (T-max) for changing the compression ratio to the upper limit compression ratio εM that can be changed by the sliding movement of the cylinder block 103. As a result, the servo motor 112 can be made smaller as the required characteristics are lowered. Even with such a small servo motor 112, the compression ratio can be changed between the lower limit compression ratio εL and the compression ratio εLm shown in the drawing without any problem.
[0063]
Incidentally, the torque characteristics shown in FIG. 9 are those in a situation where the engine load is high as described with reference to FIG. 5. However, when the engine load decreases due to the accelerator being stepped back by the driver, it becomes as follows. FIG. 10 is an explanatory diagram for explaining how the compression ratio is changed when the engine load is reduced.
[0064]
In FIG. 10, the torque characteristics (maximum torque on the negative side and positive side) of the servo motor 112 are the same as those in FIG. 9, and it is assumed that the engine load is reduced to about 85% of FIG. Is.
[0065]
When the engine load is reduced in this way, the combustion pressure P is also reduced, so that the torque required to slide the cylinder block 103 against the combustion pressure P and increase the compression ratio is reduced. For this reason, the torque diagram (high compression side torque diagram) in FIG. 10 when changing the compression ratio from the low compression ratio side to the high compression ratio side should be less than that shown in FIG. Become.
[0066]
When the target compression ratio εt is a compression ratio in the vicinity of the upper limit compression ratio εM as in the case of FIG. 9, the change from the low compression ratio to the high compression ratio side is as shown in FIG. By passing the negative determination in step S230, the compression ratio is not limited, and the compression ratio is changed to the high compression ratio side along the high compression ratio side torque diagram with εL2, εL3,.
[0067]
Even if the compression ratio becomes the compression ratio εLm in FIG. 9 where the change is restricted in FIG. 9 where the engine load is high, the combustion pressure P is also reduced due to the reduction in the engine load in FIG. Then, the negative determination remains. Therefore, the compression ratio is changed to the target compression ratio εt side along the high compression side torque diagram without being restricted in step S240. Since the motor torque of the target compression ratio εt in the high compression ratio side torque diagram is smaller than the negative side maximum torque TL-max of the motor torque characteristic shown in the figure, the drive ratio of the servo motor 112 is continuously controlled. Can be changed to the upper limit compression ratio εM or a target compression ratio εt in the vicinity thereof. That is, according to the present embodiment, when the engine load is reduced from the high load state, the compression ratio change that has been restricted under the high engine load is released, and the compression ratio is expanded over a wider range. It will be possible to change the height. In addition, such a compression ratio change can be realized by a small servo motor 112.
[0068]
The engine load state in which the engine load as described with reference to FIG. 10 is reduced from a high load (for example, about 85% reduction) can be obtained during normal driving of a vehicle equipped with the variable compression ratio engine 100. The operating range of the variable compression ratio engine 100 substantially coincides with a normal load region that is frequently requested. Therefore, when the engine load is in a load range higher than the normal load range, the change of the compression ratio is limited according to the combustion pressure P as described in FIG.
[0069]
The engine load area included in the illustrated normal engine load area is a light load to medium load load area, and the engine speed is also a low speed to medium speed area. Appear very frequently. For example, in urban driving, the engine load region appears in a range of approximately 90 to 95% during the driving process. Therefore, in such a normal vehicle running state, as described above, the compression ratio can be changed over a wide range up to the upper limit compression ratio εM or the vicinity thereof, which is preferable from the viewpoint of improving fuel consumption.
[0070]
Here, how the compression ratio is changed will be described in relation to the engine load. FIG. 11 is an explanatory diagram for explaining the state of the compression ratio change described in FIGS. 8 to 10 in association with the engine load.
[0071]
As described above, when the compression ratio is changed from the low compression ratio to the high compression ratio under a high engine load condition (see FIG. 9), the combustion pressure P is increased by increasing the compression ratio under the high engine load condition. Is equal to or higher than the specified combustion pressure P0, the compression ratio is increased to εLm (<upper limit compression ratio εM), and the compression ratio is set to the compression ratio in the intermediate region. That is, as shown in FIG. 11, in a region where the engine load is high and the rotational speed is relatively low, the compression ratio is set to a low compression ratio to avoid knocking, and the engine load is slightly lower than this region or a high engine load. In the high rotation speed region, the compression ratio becomes the compression ratio in the intermediate region (<εLm). In the region where the engine load is low, that is, in the normal load region where the request frequency is high as described above, the compression ratio can be changed up to the upper limit compression ratio εM as described in FIG. The fuel efficiency can be improved effectively.
[0072]
Next, a modified example will be described. In the above embodiment, the motor drive temporary stop / continuation control is switched according to the combustion pressure P to limit the compression ratio change to the high compression ratio side. However, the following modifications can be made. FIG. 12 is a flowchart for explaining the contents of the compression ratio change control in the first modification.
[0073]
In the first modification, the target compression ratio εt is reduced and corrected according to the combustion pressure P. That is, as shown in FIG. 12, following the calculation of the target compression ratio εt (step S110), the compression ratio change status is determined (step S111) and the combustion pressure P is read in the same manner as the limiting control in FIG. (Step S112), the combustion pressure P is compared and determined (Step S113). In the case of the change determination to the low compression ratio side in step S111 and the change determination to the high compression ratio side under the low combustion pressure in step S113, the process proceeds to step S120, and the target obtained in step S110. No change is made to the compression ratio εt. Then, following the affirmative determination in step S113, the target compression ratio εt obtained in step S110 is reduced to a compression ratio εLm that can be changed with a torque (TL-max; see FIG. 9) that can be exerted by the servo motor 112. Correction is performed (step S114). Thereby, the compression ratio is changed to the target compression ratio εt (= εLm) after the reduction correction. Even in such a modification, the compression ratio can be changed as described above even though the servo motor 112 is small.
[0074]
The following modifications are also possible. In this modification, when the target compression ratio εt of FIG. 6 is calculated (step S110), the calculation method is switched as follows according to the change state of the compression ratio. First, prior to the calculation of the target compression ratio εt, in the same way as the limit control in FIG. 8, the determination of the compression ratio change state, the reading of the combustion pressure P, and the comparison determination of the combustion pressure P are performed. In the case of changing the compression ratio to 1 and changing the compression to the high compression ratio under a low combustion pressure, the target compression ratio εt is calculated using the map of FIG. 7 as described above. If the compression ratio is changed to the high compression ratio side under a high combustion pressure, the compression ratio εLm that can be changed by the torque (TL-max; see FIG. 9) that the servo motor 112 can exert on the target compression ratio εt itself. Calculate as That is, in this case, when calculating the target compression ratio εt in step S110 in FIG. 6, the reference map is changed from that shown in FIG. 7, and a map for calculating the target compression ratio corresponding to FIG. 11 is used. To. In this way, when the compression ratio is increased under a condition where the engine load is high and the combustion pressure is high, the combustion pressure can be directly set to the compression ratio in the intermediate range shown in FIG. Even in this modification, the compression ratio can be changed as described above even though the servo motor 112 is small.
[0075]
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and embodiments, and can of course be implemented in various modes without departing from the gist of the present invention. is there.
[0076]
For example, in the above embodiment, the cylinder block 103 is slid toward the top dead center side with respect to the lower case 104 to change the compression ratio, and the control angle (cam shaft angle) of each cam shaft at that time is 0 °. Although it is set to ˜90 °, a configuration in which the cylinder block 103 is slid to the bottom dead center side can also be adopted. In this case, the control angle (cam shaft angle) of each cam shaft is −0 ° to −90 °.
[0077]
In the above-described embodiment, the compression ratio changing mechanism is constructed by combining the cam portion 109b-cylinder block 103 and the movable bearing portion 109c-lower case 104. However, the combination of the cam portion-lower case, movable bearing portion-cylinder block is used. A compression ratio changing mechanism may be constructed. Further, the shape of the cam portion 109b is preferably a perfect circle, but it can function even if it is not a perfect circle. For example, in the above-described embodiment, even if the major axis is an ellipse or an oval having the same length as the cam portion 109b, it can function.
[0078]
Furthermore, the variable compression ratio engine of the above embodiment can be easily applied to a V-type engine and a horizontally opposed engine. In this case, the pair of camshafts described above may be arranged for each bank, or in the case of a V-type engine, a pair of camshafts are arranged at the bases of both banks so that the central angle formed by both banks The compression ratio may be changed by sliding the entire V-shaped bank in the central direction.
[0079]
Moreover, it can also be set as the following modifications. As described with reference to FIG. 10, in the variable compression ratio engine 100 of the present embodiment, the upper and lower limits can be realized by the sliding movement of the cylinder block 103 when the servo motor 112 is downsized and the engine load is reduced. The compression ratio can be changed within the range. Therefore, after adopting the small servo motor 112, the engine load is deformed to limit the engine load. In this way, the compression ratio can always be changed within the range of the upper and lower limit compression ratios with the small servo motor 112. Therefore, when the variable compression ratio engine 100 of this modification is applied to a hybrid vehicle, there are the following advantages.
[0080]
In such a hybrid vehicle, since the driving force of the electric motor can be used together with the engine power, the variable compression ratio engine 100 is operated with a restriction on the engine load. Assist with the driving force of the motor. In this way, in addition to downsizing the servo motor 112, it is possible to suitably execute improvement in fuel consumption and avoidance of knocking by changing the compression ratio over a wide range.
[Brief description of the drawings]
FIG. 1 is a schematic exploded perspective view of a variable compression ratio engine 100 according to a first embodiment.
FIG. 2 is a schematic perspective view showing a schematic configuration of the variable compression ratio engine 100. FIG.
FIG. 3 is an explanatory diagram for explaining the state of device driving when the compression ratio is changed in the variable compression ratio engine 100. FIG.
4 is a block diagram schematically illustrating a device configuration involved in compression ratio change control of the variable compression ratio engine 100. FIG.
FIG. 5 is an explanatory diagram showing the relationship between various torques involved in changing the compression ratio under a situation where the load required for the engine (engine load) is high.
FIG. 6 is a flowchart showing compression ratio change control.
FIG. 7 is an explanatory diagram for explaining the content of compression ratio control.
FIG. 8 is a flowchart showing the contents of control for limiting the compression ratio change.
FIG. 9 is an explanatory diagram illustrating a change in the compression ratio when the change in the compression ratio is restricted while showing the relationship of the torque in FIG. 5 when the engine load is high.
FIG. 10 is an explanatory diagram for explaining how the compression ratio is changed when the engine load is reduced.
FIG. 11 is an explanatory diagram for explaining the state of the compression ratio change described with reference to FIGS. 8 to 10 in association with the engine load.
FIG. 12 is a flowchart illustrating the content of compression ratio change control in a modified example.
[Explanation of symbols]
100: Variable compression ratio engine
102 ... Cylinder
103 ... Cylinder block
104 ... Lower case
105 ... Cam storage hole
106 ... Bolt
107 ... Cap
108 ... Bearing housing hole
109 ... Cam shaft
109a ... Shaft
109b ... cam part
109c. Movable bearing part
109d ... Mounting part
110 ... Worm wheel
111a, 111b ... Warm
112 ... Servo motor
115 ... Crankshaft
130 ... Uplift
132 ... Standing wall
161: Throttle sensor
162 ... accelerator sensor
163 ... Rotation speed / crank angle sensor
164 ... Motor rotation angle sensor

Claims (4)

When changing the compression ratio, the rotational driving force of the driving source is transmitted to the compression ratio changing mechanism, and at least one of the engine member on the piston head side and the engine member on the crankcase side is driven by the compression ratio changing mechanism. , A compression ratio control method in an internal combustion engine for changing a relative positional relationship between the two engine members to change a combustion chamber volume and changing a compression ratio,
Setting a target compression ratio according to the operating state of the internal combustion engine;
When changing the compression ratio to the target compression ratio on the high compression ratio side, the step of limiting the change of the compression ratio to the high compression ratio side according to the force resulting from the combustion pressure of the fuel in the combustion chamber A compression ratio control method. An internal combustion engine that changes the compression ratio,
A driving source for generating a rotational driving force for changing the compression ratio;
A transmission means for transmitting the rotational driving force;
By driving at least one of the engine member on the piston head side and the engine member on the crankcase side by the transmission driving force from the transmission means, the relative positional relationship between the engine members is changed and the combustion chamber volume is changed. A compression ratio changing mechanism that changes the compression ratio,
Drive source control means for controlling the drive source so that the compression ratio becomes a target compression ratio determined according to the operating state of the internal combustion engine,
The drive source control means includes
When changing the compression ratio to the target compression ratio on the high compression ratio side, compression that restricts the change of the compression ratio to the high compression ratio side according to the force resulting from the combustion pressure of the fuel in the combustion chamber An internal combustion engine having a ratio limiting means. An internal combustion engine according to claim 2,
The compression ratio limiting means is
An internal combustion engine that operates when the compression ratio is changed to a high compression ratio in a load range in which the load of the internal combustion engine is higher than a normal load range that is frequently requested during operation of the internal combustion engine. An internal combustion engine that changes the compression ratio,
A driving source for generating a driving force for changing the compression ratio;
Transmission means for transmitting the driving force;
By driving at least one of the engine member on the piston head side and the engine member on the crankcase side by the transmission driving force from the transmission means, the relative positional relationship between the engine members is changed to change the combustion chamber volume. A compression ratio changing mechanism that changes the compression ratio,
Drive source control means for controlling the drive source to cause the compression ratio change by the compression ratio change mechanism,
The drive source control means includes
In a situation where the compression ratio is changed to the high compression ratio side in a higher load range than the normal load range, which is frequently required when operating the internal combustion engine, the drive source is transmitted to the compression ratio change mechanism via the transmission means. An internal combustion engine that changes the compression ratio toward the high compression ratio within a possible transmission torque range and sets the compression ratio to an intermediate compression ratio lower than the highest compression ratio that can be changed by the compression ratio changing mechanism.

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