Patent Publication Number: US-9850813-B2

Title: Variable compression ratio internal combustion engine

Description:
TECHNICAL FIELD 
     The present invention relates to a control device for a variable compression ratio internal combustion engine provided with a variable compression ratio mechanism capable of changing an engine compression ratio in accordance with a rotational position of a control shaft. 
     BACKGROUND ART 
     Patent document 1 discloses an internal combustion engine (hereinafter referred to as “variable compression ratio internal combustion engine”) provided with a variable compression ratio mechanism capable of changing an engine compression ratio in accordance with a rotational position of a control shaft. A speed reducing mechanism is provided between the control shaft and an actuator such as a motor that drives the control shaft. A rotation shaft, which is linked through a lever to the control shaft, is provided in the speed reducing mechanism. For example, the rotation shaft is rotatably supported in a housing fixed to an engine body. 
     CITATION LIST 
     Patent Literature 
     Patent document 1: Japanese Patent Provisional Publication No. JP2013-253512 
     SUMMARY OF INVENTION 
     Technical Problem 
     In such a variable compression ratio internal combustion engine, a high compression ratio side regulation part and a low compression ratio side regulation part are provided in the housing that rotatably supports the rotation shaft, for mechanically regulating a rotatable range of the rotation shaft between a high compression ratio side and a low compression ratio side. Also, compression ratio reference position learning operation is carried out, based on a detection signal from a rotation sensor that detects a rotational position of the rotation shaft, in a state where the rotational position of the rotation shaft has been regulated and positioned mechanically by means of either of these two regulation parts. 
     However, the regulation parts and the rotation sensor are provided in the same housing, and thus there is a possibility that the detection accuracy of the rotation sensor deteriorates owing to vibrations, deformation and the like, occurring when the control shaft is brought into collision with a stopper face of each of the regulation parts, thus resulting in a deterioration in the compression ratio reference position learning accuracy. 
     It is, therefore, in view of the previously-described circumstances, an object of the present invention to improve the compression ratio reference position learning accuracy in a variable compression ratio internal combustion engine provided with a variable compression ratio mechanism. 
     Solution to Problem 
     A variable compression ratio internal combustion engine of the present invention includes a control shaft rotatably supported by an engine body, a variable compression ratio mechanism for changing an engine compression ratio in accordance with a rotational position of the control shaft, an actuator that rotatively drives the control shaft, and a speed reducing mechanism for reducing a rotational power of the actuator and for transmitting the speed-reduced power to the control shaft. The speed reducing mechanism has a rotation shaft rotatably supported in a housing fixed to the engine body and a lever that connects the rotation shaft and the control shaft. 
     The variable compression ratio internal combustion engine has a first regulation part located in the engine body for mechanically regulating the control shaft to a position of maximum rotation on one side of a low compression ratio side and a high compression ratio side and a second regulation part located in the housing for mechanically regulating the rotation shaft to a position of maximum rotation on the other side of the low compression ratio side and the high compression ratio side. 
     The first regulation part is configured to regulate the control shaft to the position of maximum rotation on the high compression ratio side, whereas the second regulation part is configured to regulate the rotation shaft to the position of maximum rotation on the low compression ratio side. 
     Preferably, the variable compression ratio internal combustion engine has a rotation sensor for detecting a rotational position of one shaft of the control shaft and the rotation shaft, and a reference position learning means for carrying out compression ratio reference position learning operation, based on a detection signal from the rotation sensor, in a state where the other shaft of the control shaft and the rotation shaft has been mechanically regulated by either the first regulation part or the second regulation part. 
     Advantageous Effects of Invention 
     According to the present invention, the first regulation part and the second regulation part are located individually on the engine body side where the control shaft is installed and on the housing side where the rotation shaft is installed, for regulating a rotatable range between the high compression ratio side and the low compression ratio side. Hence, the degree of freedom in layout is high. For instance when carrying out compression ratio reference position learning operation through the use of the rotation sensor, it is possible to suppress a deterioration in the detection accuracy of the rotation sensor by bringing either the control shaft or the rotation shaft into a mechanically-regulated state by means of the regulation part not provided with the rotation sensor, thus improving the compression ratio reference position learning accuracy. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram schematically illustrating the configuration of a control device for a variable compression ratio internal combustion engine provided with a variable compression ratio mechanism in one embodiment to which the invention is applied. 
         FIG. 2  is a diagram schematically illustrating the configuration of the control device for the variable compression ratio internal combustion engine of the embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter explained in reference to  FIGS. 1 to 2  is a control device for a variable compression ratio internal combustion engine  1  provided with a variable compression ratio mechanism  10  in one embodiment according to the present invention. 
     With reference to  FIG. 1 , variable compression ratio internal combustion engine  1  is mainly constructed by a cylinder block  2  serving as an engine body and a cylinder head  3  fixed onto the cylinder block  2 . A piston  5  is liftably (slidably) fitted into a cylinder  4  of the cylinder head  3 . 
     Variable compression ratio mechanism  10  has a lower link  11 , an upper link  12 , a control shaft  13 , and a control link  14 . The lower link is rotatably installed on a crankpin  7  of a crankshaft  6 . The upper link is configured to connect the lower link  11  and the piston  5 . The control shaft is rotatably supported on the cylinder block  2 . The control link is configured to connect the control shaft  13  and the lower link  11 . The upper end of upper link  12  and the piston  5  are connected to each other by means of a piston pin  15  so as to permit relative rotation between them. Upper link  12  and lower link  11  are connected to each other by means of a first connecting pin  16  so as to permit relative rotation between them. Lower link  11  and the upper end of control link  14  are connected to each other by means of a second connecting pin  17  so as to permit relative rotation between them. The lower end of lower link  11  is rotatably installed on a control eccentric shaft  18  provided eccentrically to a journal portion  13 A serving as the rotation center of control shaft  13 . 
     As shown in  FIG. 2 , a speed reducing mechanism  22  is interposed in a power-transmission path between the control shaft  13  and an output shaft  21 A of a motor  21 , serving as an actuator that rotatively drives the control shaft  13 , for reducing a rotational power of the output shaft  21 A of motor  21  and for transmitting the speed-reduced power to the control shaft  13 . Speed reducing mechanism  22  has a speed reducer  23  such as a wave motion gear device that provides high reduction ratios, a rotation shaft  24  that rotates integrally with the output shaft of speed reducer  23 , and a lever  25  configured to connect the rotation shaft  24  and the control shaft  13  (see  FIG. 1 ). Rotation shaft  24  is accommodated and arranged inside of a housing  26  fixedly connected to and located alongside the cylinder block  2 . The rotation shaft is rotatably supported inside of the housing  26  and arranged parallel to the control shaft  13 . Lever  25  is structured to extend through slits of cylinder block  2  and housing  26 . 
     One end of lever  25  and the top end of a first arm  27  extending radially from the journal portion  13 A of control shaft  13  are connected to each other by means of a third connecting pin  28  so as to permit relative rotation between them. The other end of lever  25  and the top end of a second arm  29  extending radially from a journal portion  24 A serving as the rotation center of rotation shaft  24  are connected to each other by means of a fourth connecting pin  30  so as to permit relative rotation between them. 
     In the variable compression ratio mechanism  10  constructed as discussed above, when the rotational position of control shaft  13  is changed by means of the motor  21  through the speed reducing mechanism  22 , a change in the attitude of lower link  11  occurs and thus a change in stroke characteristic of piston  5  including a piston top dead center (TDC) position and a piston bottom dead center (BDC) position occurs. In this manner, an engine compression ratio is continuously changed. 
     With reference to  FIG. 2 , as a compression ratio detection unit that detects an actual compression ratio which is an actual engine compression ratio, a rotation sensor  31  is installed on the housing  26  for detecting a rotational position of rotation shaft  24  corresponding to the actual compression ratio, that is, a compression ratio reference position. Also, a motor speed detection sensor  32  is installed on the motor  21  for detecting a motor speed. 
     A control unit  33  is a digital computer system capable of storing and executing various control processes. The control unit is configured to output control signals to various actuators based on an engine operating condition detected by sensors  31 ,  32  and the like, for integrally controlling respective operations of these actuators. Concretely, the control unit is configured to control driving of a variable valve timing mechanism  34  capable of changing intake valve timing (or exhaust valve timing), for controlling intake valve open timing (IVO) and intake valve closure timing (IVC). Also, the control unit is configured to control driving of a spark plug  35  that spark-ignites an air-fuel mixture in the combustion chamber, for controlling ignition timing. Furthermore, the control unit is configured to control driving of an electronically-controlled throttle  36  that opens or closes an intake-air passage, for controlling throttle opening. 
     Additionally, control unit  33  is configured to set a target compression ratio based on the engine operating condition, and feedback-control the operation of motor  21  for maintaining the deviation between the target compression ratio and the actual compression ratio detected by the rotation sensor  31  as small as possible. 
     As schematically shown in  FIG. 1 , a rotatable range of each of control shaft  13  and rotation shaft  24 , both linked together in a manner so as to rotate in conjunction with each other, is mechanically regulated or limited by means of a low compression ratio side stopper face  41  serving as a low compression ratio side regulation part and a high compression ratio side stopper face  42  serving as a high compression ratio side regulation part. For instance, in the shown embodiment, the low compression ratio side stopper face  41  is provided inside of the housing  26 . When rotation shaft  24  rotates toward a maximum low compression ratio side (i.e., in the direction indicated by the arrow “Y 1 ” in  FIG. 1 ), a side face of the second arm  29  is brought into abutted-engagement with the low compression ratio side stopper face  41 . Hence, control shaft  13  and rotation shaft  24  are structured to be mechanically locked up and regulated at a low compression ratio side stopper position. On the other hand, the high compression ratio side stopper face  42  is provided inside of the cylinder block  2 . When control shaft  13  rotates toward a maximum high compression ratio side (i.e., in the direction indicated by the arrow “Y 2 ” in  FIG. 1 ), a side face of the first arm  27  is brought into abutted-engagement with the high compression ratio side stopper face  42 . Hence, control shaft  13  and rotation shaft  24  are also structured to be mechanically locked up and regulated at a high compression ratio side stopper position. 
     When a predetermined engine operating condition for carrying out initializing operation for rotation sensor  31  is satisfied (for example, immediately after an engine start or immediately before an engine stop), the initializing operation is carried out. In this initializing operation, for instance in a state where, with the rotation shaft  24  in abutted-engagement with the high compression ratio side stopper face  42 , control shaft  13  has been mechanically regulated and locked up at the high compression ratio side stopper position serving as a reference position, a detected value of rotation sensor  31 , corresponding to an actual compression ratio, is learned and initialized to a given initial value corresponding to the compression ratio reference position. By virtue of the learning and initializing operation, the correspondence relation between an actual rotational position of each of control shaft  13  and rotation shaft  24  and an actual compression ratio detected by rotation sensor  31  can be reset to an initial normal state. 
     The specified configuration of the embodiment and its operation and effects are hereunder enumerated. 
     (1) The variable compression ratio internal combustion engine has a high compression ratio side stopper face  42  located in the cylinder block  2  (serving as an engine body) and serving as a first regulation part (a first regulation structure) for mechanically regulating the control shaft  13  to a position of maximum rotation on one side of a low compression ratio side and a high compression ratio side and a low compression ratio side stopper face  41  located in the housing  26  and serving as a second regulation part (a second regulation structure) for mechanically regulating the rotation shaft  24  to a position of maximum rotation on the other side of the low compression ratio side and the high compression ratio side. In this manner, the high compression ratio side stopper face  42  and the low compression ratio side stopper face  41  are located individually on the side of control shaft  13  and on the side of rotation shaft  24 , thus increasing the degree of freedom in layout. As described later, when carrying out compression ratio reference position learning operation, one shaft of the control shaft  13  and the rotation shaft  24 , the one shaft being equipped with the rotation sensor  31 , and the other shaft of the control shaft and the rotation shaft, the other shaft being configured such that a rotational position of the other shaft is mechanically regulated by means of either the stopper face  41  or the stopper face  42 , can be different from each other. Hence, it is possible to carry out the learning operation without being affected by vibrations and deformation, caused by abutment-engagement of the other shaft with the stopper face, thus improving the detection accuracy during learning operation. 
     (2) In the shown embodiment, the high compression ratio side stopper face  42 , serving as the first regulation part, is configured to regulate the control shaft  13  to the position of maximum rotation on the high compression ratio side, whereas the low compression ratio side stopper face  41 , serving as the second regulation part, is configured to regulate the rotation shaft  24  to the position of maximum rotation on the low compression ratio side. That is, when carrying out learning operation, collision noise caused by collision with the stopper face can be reduced via an oil pan of the engine body by mechanically regulating the control shaft  13  by the high compression ratio side stopper face  42  provided on the engine body side, as compared to regulating action on the housing side. This contributes to a suppression of collision noise during learning operation. The learning operation is carried out or initiated by bringing the shaft into abutted-engagement with only one of the stopper faces  41 ,  42 , thus shortening the learning time. 
     (3) Rotation sensor  31  is provided for detecting a rotational position of one shaft of the control shaft  13  and the rotation shaft  24 . Compression ratio reference position learning operation is executed, based on a detection signal from the rotation sensor  31 , in a state where the other shaft of the control shaft  13  and the rotation shaft  24  has been mechanically regulated by means of either the first regulation part or the second regulation part. As discussed above, when carrying out compression ratio reference position learning operation, one shaft of the control shaft  13  and the rotation shaft  24 , the one shaft being equipped with the rotation sensor  31 , and the other shaft of the control shaft and the rotation shaft, the other shaft being configured such that a rotational position of the other shaft is mechanically regulated by either the stopper face  41  or the stopper face  42 , can be different from each other. Hence, it is possible to carry out the learning operation without being affected by vibrations and deformation, caused by abutment-engagement of the other shaft with either the stopper face  41  or the stopper face  42 , thus improving the detection accuracy during learning operation. 
     (4) Also, in the shown embodiment, rotation sensor  31  is configured to detect the rotational position of the rotation shaft  24 . The compression ratio reference position learning operation is carried out, based on the detection signal from the rotation sensor, in a state where the control shaft  13  has been mechanically regulated by the high compression ratio side stopper face  42 . 
     On the high compression ratio side, a variation in compression ratio with respect to a rotational angle of control shaft  13  is great. Hence, by executing the learning operation on the high compression ratio side on which a very high compression ratio control accuracy is required, it is possible to improve the control accuracy on the high compression ratio side. Thus, it is possible to suppress knocking from occurring on the high compression ratio side. Additionally, it is possible to suppress the valves and the piston from excessively approaching each other, even on the high compression ratio side that the valves and the piston tend to approach each other. 
     Also, the variable compression internal combustion engine is configured such that the rotational position of rotation shaft  24  is detected by rotation sensor  31 , while regulating the rotational position on the side of control shaft  13 . Thus, individual differences of a link length, a shaft hole, a connecting-pin clearance and the like in a power-transmission path between the control shaft  13  and the rotation shaft  24  can be cancelled or absorbed, thereby improving the control accuracy. 
     Furthermore, during operation at the lowest compression ratio, in which a maximum load is applied, in order to reduce a compression-ratio holding torque of motor  21 , it is effective to increase (preferably, to maximize) a reduction ratio between the control shaft  13  and the rotation shaft  24 . Assuming that the low compression ratio side stopper face is set on the side of control shaft  13 , an excessive motor torque, multiplied owing to an excessive reduction ratio, tends to act on the low compression ratio side stopper face. This may result in abrasion and breakage of the low compression ratio side stopper face. In the shown embodiment, the low compression ratio side stopper face  41  is provided on the side of rotation shaft  24 . Hence, there is a less tendency for an excessive torque multiplied at the reduction ratio to be applied the stopper face  41 , and thus it is possible to protect the low compression ratio side stopper face  41 . 
     (5) Rotation shaft  24  is set so that the rotation shaft  24  is positioned within a predetermined angular range containing a rotational position such that torque about the rotation shaft, which torque is transmitted from the control shaft  13  through the lever  25  to the rotation shaft  24 , becomes a minimum in a state where the rotation shaft  24  has been mechanically regulated by the low compression ratio side stopper face  41 . Structurally, the torque about the rotation shaft  24 , transmitted from the control shaft  13  through the lever  25  to the rotation shaft  24 , tends to decrease, as the angle θ between the link centerline  25 A of lever  25  (i.e., the line segment connecting the center of the third connecting pin  28  and the center of the fourth connecting pin  30 ) and the link centerline  29 A of the second arm  29  (i.e., the line segment connecting the center of the journal portion  24 A of rotation shaft  24  and the center of the fourth connecting pin  30 ) decreases. Therefore, For the above reason, in a state where control shaft  13  as well as rotation shaft  24  has been locked up at the low compression ratio side stopper position, the rotation shaft  24  is set such that the rotation shaft  24  is positioned within a predetermined angular range containing a specified position at which the angle θ becomes a minimum (in other words, when the link centerline  25 A and the link centerline  29 A are brought into line with each other). 
     Hereby, even when normal compression ratio control becomes disable for some reason during high load operation at which large combustion load is applied or during high speed operation at which large inertial load is applied, after having been reduced to the compression ratio at the low compression ratio side stopper position by virtue of combustion pressure, it is possible to stably hold or maintain the low compression ratio state at the low compression ratio stopper position, while suppressing torque applied from control shaft  13  to the rotation shaft  24 . Additionally, even when a fluctuating torque is applied from the control shaft  13  to the rotation shaft  24 , it is possible to reduce collision-contact of the rotation shaft  24  with the low compression ratio side stopper face  41 , thus suppressing collision noise, caused by the collision-contact, and consequently suppressing the occurrences of abrasion and impression. 
     (6) A surface accuracy of the high compression ratio side stopper face is set higher than a surface accuracy of the low compression ratio side stopper face. Hence, it is possible to relax the surface accuracy of the low compression ratio side stopper face  41 , while ensuring the surface accuracy of the high compression ratio side stopper face  42  used for learning control. For instance, surface finishing of the low compression ratio side stopper face  41  can be eliminated, thereby improving the productivity due to reduced manufacturing man-hour and enabling lower costs.