Engine of compression-ratio variable type

Information

  • Patent Grant
  • 6820577
  • Patent Number
    6,820,577
  • Date Filed
    Tuesday, October 21, 2003
    21 years ago
  • Date Issued
    Tuesday, November 23, 2004
    20 years ago
Abstract
In an engine of a compression-ratio variable type, a subsidiary rod and a piston connected to a crankshaft are connected to each other through a connecting rod, and an eccentric shaft mounted at an eccentric location on a support shaft turnably carried in an engine body and the subsidiary rod are connected to each other through a control rod, so that the compression ratio of the engine is changed by changing the turned position of the support shaft. The engine further includes a one-way clutch mounted between the support shaft and the engine body for limiting the direction of turning of the support shaft. The turned position of the support shaft is limited selectively at a plurality of points by a turned-position limiting means, and a load applied to at least one of the support shaft and the turned-position limiting means is moderated by buffering means.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




The present invention relates to an engine of a compression-ratio variable type, comprising a connecting rod connected at one end to a piston through a piston pin, a subsidiary rod connected to a crankshaft through a crankpin and to the other end of the connecting rod, a control rod connected at one end to the subsidiary rod at a location displaced from a connected position of the connecting rod, a support shaft turnably carried in an engine body, and an eccentric shaft mounted at an eccentric location on the support shaft and connected to the other end of the control rod, the turned position of the support shaft being changed to change the compression ratio.




2. Description of the Related Art




There is a conventional engine of a compression-ratio variable type known from, for example, Japanese Patent Application Laid-open No. 9-228858, in which a subsidiary rod connected to a crankshaft and a piston are connected to each other through a connecting rod, and an eccentric shaft mounted at an eccentric location on a support shaft turnably carried in an engine body and the subsidiary rod are connected to each other through a control rod, the compression ratio of the engine being changed by changing the turned position of the support shaft.




In the conventional engine, the turned position of the support shaft is changed by driving the support shaft in turning by an actuator such as an electric motor and a cylinder, to thereby change the compression ratio. However, an expansion load and a compression load are applied to the control rod by the combustion in the engine and inertia. For this reason, a shock load is applied to the actuator such as the electric motor and the cylinder and hence, a means for moderating such a shock must be mounted between the actuator and the support shaft, resulting in a complicated arrangement.




If the direction of turning of the support shaft is limited to one direction, the support shaft can be turned utilizing the expansion load and the compression load applied to the control rod by the combustion in the engine and the inertia. With this arrangement, the actuator for driving the support shaft in turning is not required. However, a limiting means for limiting the turned position of the support shaft at a plurality of points is required, and when the turned position of the support shaft is limited, a shock is applied to contact portions of such a limiting means and the support shaft, so that it is necessary to moderate such a shock.




SUMMARY OF THE INVENTION




Accordingly, it is an object of the present invention to provide an engine of a compression-ratio variable type, wherein the support shaft is turned utilizing the combustion in the engine and the inertia, and moreover, the shock generated upon limiting of the turned position of the support shaft can be moderated in a simple arrangement.




To achieve the above object, according to a first feature of the present invention, there is provided an engine of a compression-ratio variable type, comprising a connecting rod connected at one end to a piston through a piston pin, a subsidiary rod connected to a crankshaft through a crankpin and to the other end of the connecting rod, a control rod connected at one end to the subsidiary rod at a location displaced from a connected position of the connecting rod, a support shaft turnably carried in an engine body, and an eccentric shaft mounted at an eccentric location on the support shaft and connected to the other end of the control rod, the turned position of the support shaft being changed to change the compression ratio, wherein the engine further includes a one-way clutch mounted between the support shaft and the engine body in such a manner that the direction of turning of the support shaft is limited, a turned-position limiting means for limiting the turned position of the support shaft selectively at a plurality of points, and buffering means for moderating a load applied to at least one of the support shaft and the turned-position limiting means upon changing-over of the compression ratio.




With such arrangement of the first feature, an expansion load and a compression load are applied to the control rod by the combustion in the engine and inertia, whereby the support shaft and the eccentric shaft are turned in the direction limited by the one-way clutch, when the compression ratio is changed over. Therefore, an actuator for directly turning the support shaft is not required. Moreover, the load applied to at least one of the support shaft and the turned-position limiting means when the compression ratio is changed over, can be moderated by the buffering means.




According to a second feature of the present invention, in addition to the first feature, a flywheel is secured to the crankshaft so that a rotational force is transmitted from a recoil starter to the flywheel in response to the starting operation of the engine; the buffering means comprises an output member disposed coaxially with the crankshaft in such a manner that the rotational force in the same direction as that of the recoil starter can be transmitted to the flywheel, and the rotation thereof is limited when the recoil starter is not operated, an input member coaxial with the output member, and a spiral spring mounted between the output member and the input member; and a torque transmitting means is mounted between the support shaft and the input member so that it transmits the rotational force in a direction to wind up the spiral spring from the support shaft to the input member until the completion of the winding-up of the spiral spring, but it permits the support shaft to be raced after the completion of the winding-up of the spiral spring.




With such arrangement of the second feature, when the compression ratio is changed over, the rotational torque of the support shaft is transmitted to the input member of the buffering means through the torque transmitting means, whereby forces are accumulated in the spiral spring by the winding-up of the spiral spring, and the moderation of a shock can be achieved by absorbing a load applied to the support shaft by the spiral spring. Namely, while the support shaft is turned to a next turning-inhibited position by the turned-position limiting means when the compression ratio is changed over, the rotational torques applied to the support shaft can be buffered and accumulated by the spiral spring of the buffering means. During accumulation of the force in the spiral spring, the rotation of the output member is limited, and when the recoil starter is started at the next start of the engine, the spring force accumulated in the spiral spring is transmitted from the output member to the flywheel. Thus, even if the expansion load on the recoil starter is alleviated, the engine can be started sufficiently.




According to a third feature of the present invention, in addition to the arrangement of the first feature, limiting abutments are provided on the support shaft at a plurality of points axially spaced apart from each other with their positions displaced in a circumferential direction of the support shaft; an actuator is connected to a limiting member for driving the limiting member in turning, the limiting member being carried in the engine body to constitute a portion of the turned-position limiting means so that it can be turned about an axis perpendicular to the support shaft to come into abutment alternatively against one of the limiting abutments to limit the turned position of the support shaft; and the buffering means is interposed between the limiting member and the engine body in order to moderate an axial shock upon the abutment of the alternatively selected limiting abutment against the limiting member.




With such arrangement of the third feature, the turned position of the support shaft can be limited in such a manner that the limiting member is brought into abutment against one of the plurality of limiting abutments provided on the support shaft by turning the limiting member by the actuator, whereby the compression ratio can be changed. In this case, a shock in a direction perpendicular to the support shaft is applied to the limiting member by the contact between the limiting member and one of the limiting abutments, but the shock can be moderated by a simple arrangement in which the buffering means is interposed between the limiting member and the engine body. Thus, it is possible to avoid the application of the shock to the actuator for driving the limiting member and to enhance the durability reliability, while avoiding an increase in sizes of various members such as the support shaft and the limiting member due to increases in their strengths. Moreover, it is also possible to suppress to a low level a sound generated when the limiting member is brought into contact with one of the limiting abutments.




According to a fourth feature of the present invention, in addition to the first feature, the buffering means is mounted between the support shaft and the engine body to moderate the radial load applied from the control rod to the support shaft.




With such arrangement of the fourth feature, when the compression ratio is changed over, a large load is applied to the support shaft and the turned-position limiting means, but the radial load applied to the support shaft is moderated by the buffering means. Therefore, it is possible to enhance the durability reliability, while avoiding increases in sizes of various members such as the support shaft and the turned-position limiting means due to increases in their strengths. Moreover, it is also possible to suppress to a low level a sound generated when the turned position is limited by the turned-position limiting means.




The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a front view of an engine.





FIG. 2

is a sectional view taken along a line


2





2


in FIG.


1


.





FIG. 3

is a sectional view taken along a line


3





3


in FIG.


2


.





FIG. 4

is a sectional view taken along a line


4





4


in FIG.


2


.





FIG. 5

is an enlarged sectional view taken along a line


5





5


in FIG.


2


.





FIG. 6

is a partially cutaway plan view taken along a line


6





6


in

FIG. 1

in a light load state.





FIG. 7

is a view similar to

FIG. 6

, but in a heavy load state.





FIG. 8

is an enlarged sectional view showing an area in the vicinity of one end of a support shaft shown in FIG.


2


.





FIG. 9

is a sectional view taken along a line


9





9


in FIG.


8


.





FIG. 10

is an enlarged view showing an area on the side of the other end of the support shaft and an area in the vicinity of a buffering/accumulating means shown in FIG.


2


.





FIG. 11

is a sectional view taken along a line


11





11


in FIG.


10


.





FIG. 12

is an enlarged view showing an area in the vicinity of a torque transmitting means shown in FIG.


10


.





FIG. 13

is a sectional view taken along a line


13





13


in FIG.


12


.





FIG. 14

is a sectional view taken along a line


14





14


in FIG.


2


.











DESCRIPTION OF THE PREFERRED EMBODIMENT




The present invention will now be described by way of a preferred embodiment with reference to

FIGS. 1

to


14


.




Referring first to

FIGS. 1

to


3


, an engine according the embodiment is an air-cooled single-cylinder engine used, for example, in a working machine or the like, and has an engine body


21


which comprises: a crankcase


22


; a cylinder block


23


slightly inclined upwards and protruding from one side of the crankcase


22


; and a cylinder head


24


coupled to a head of the cylinder block


23


. A large number of air-cooling fins


23




a


and


24




a


are provided on outer surfaces of the cylinder block


23


and the cylinder head


24


. The crankcase


22


is installed on a cylinder head of any working machine via an installation surface


22




a


of its lower face.




The crankcase


22


comprises a case body


25


formed integrally with the cylinder block


23


by casting, and a side cover


26


coupled to an open end of the case body


25


. One end


27




a


of a crankshaft


27


protrudes from the side cover


26


. A ball bearing


28


and an oil seal


30


are interposed between the one end


27




a


of the crankshaft


27


and the side cover


26


. The other end


27




b


of the crankshaft


27


protrudes from the case body


25


. A ball bearing


29


and an oil seal


31


are interposed between the other end


27




b


of the crankshaft


27


and the case body


25


.




A flywheel


32


is secured to the other end


27




b


of the crankshaft


27


outside the case body


25


. A cooling fan


33


for supplying cooling air to various portions of the engine body


21


is secured to the flywheel


32


. A recoil starter


34


is disposed outside the cooling fan


33


.




A cylinder bore


39


is formed in the cylinder block


23


, and slidably receives therein a piston


38


. A combustion chamber


40


is formed between the cylinder block


23


and the cylinder head


24


, so that a top of the piston


38


faces the combustion chamber


40


.




An intake port


41


and an exhaust port


42


capable of leading to the combustion chamber


40


are formed in the cylinder head


24


. Disposed in the cylinder head


24


are an intake valve


43


openable and closable for providing connection and disconnection between the intake port


41


and the combustion chamber


40


as well as an exhaust valve


44


openable and closable for providing connection and disconnection between the exhaust port


42


and the combustion chamber


40


. A spark plug


45


is threadedly mounted to the cylinder head


24


with its electrodes facing the combustion chamber


40


.




A carburetor


35


is connected to an upper portion of the cylinder head


24


. A downstream end of an intake passage


46


of the carburetor


35


communicates with the intake port


41


. An intake pipe


47


leading to an upstream end of the intake passage


46


is connected to the carburetor


35


, and also connected to an air cleaner (not shown). An exhaust pipe


48


leading to the exhaust port


42


is connected to an upper portion of the cylinder head


24


, and also connected to an exhaust muffler


49


. Further, a fuel tank


51


is disposed above the crankcase


22


, so that it is supported on the crankcase


22


.




A driving gear


52


is formed integrally on the crankshaft


27


at a portion of the crankcase


22


closer to the side cover


26


. A driven gear


53


meshed with the driving gear


52


is secured to a camshaft


54


which is rotatably carried in the crankcase


22


and which has an axis parallel to the crankshaft


27


. A rotational power from the crankshaft


27


is transmitted at a reduction ratio of 1/2 to the camshaft


54


by the driving gear


52


and the driven gear


53


meshed with each other.




An intake cam


55


and an exhaust cam


56


corresponding to the intake valve


43


and the exhaust valve


44


respectively are provided on the camshaft


54


. A follower piece


57


operably carried in the cylinder block


23


is in sliding contact with the intake cam


55


. On the other hand, an operating chamber


58


is formed in the cylinder block


23


and the cylinder head


24


, so that an upper portion of the follower piece


57


protrudes into a lower portion of the operating chamber


58


. A lower end of a pushrod


59


disposed in the operating chamber


58


is in abutment against the follower piece


57


. On the other hand, a rocker arm


60


is swingably carried in the cylinder head


24


with one end abutting against an upper end of the intake valve


43


biased in a closing direction by a spring. An upper end of the pushrod


59


is in abutment against the other end of the rocker arm


60


. Thus, the pushrod


59


is operated axially in response to the rotation of the intake cam


55


, and the intake valve


43


is opened and closed by the swinging movement of the rocker arm


60


caused in response to the operation of the pushrod


59


.




A similar mechanism similar to that between the intake cam


55


and the intake valve


43


is also interposed between the exhaust cam


56


and the exhaust valve


44


, so that the exhaust valve


44


is opened and closed in response to the rotation of the exhaust cam


56


.




Referring also to

FIG. 4

, the piston


38


, the crankshaft


27


and an eccentric shaft


61


carried in the crankcase


22


of the engine body


21


for displacement in a plane passing through a cylinder axis C and perpendicular to the axis of the crankshaft


27


, are connected to one another through a link mechanism


62


.




The link mechanism


62


comprises a connecting rod


64


connected at one end to the piston


38


through a piston pin


63


, a subsidiary rod


68


connected to the crankshaft


27


through a crankpin


65


and turnably connected to the other end of the connecting rod


64


, and a control rod


69


which is turnably connected at one end to the subsidiary rod


68


at a location displaced from a connected position of the connecting rod


64


, and at the other end to eccentric shaft


61


.




The subsidiary rod


68


has, at its intermediate portion, a first semicircular bearing portion


70


which is in sliding contact with a half of a periphery of the crankpin


65


, and a pair of bifurcations


71


and


72


are provided integrally at opposite ends of the subsidiary rod


68


, so that the other end of the connecting rod


64


and one end of the control rod


69


are sandwiched between the bifurcations


71


and


72


. A second semicircular bearing portion


74


of a crank cap


73


is in sliding contact with the remaining half of the periphery of the crankpin


65


, and the crank cap


73


is fastened to the subsidiary rod


68


.




The connecting rod


64


is turnably connected at the other end to one end of the subsidiary rod


68


through a cylindrical connecting rod pin


75


. The opposite ends of the connecting rod pin


75


press-fitted into the other end of the connecting rod


64


, are turnably fitted into the bifurcation


71


at the one end of the subsidiary rod


68


.




One end of the control rod


69


is turnably connected through a subsidiary rod pin


76


to the other end of the subsidiary rod


68


. The opposite ends of the subsidiary rod pin


76


, which is relatively turnably passed through one end of the control rod


69


inserted into the bifurcation


72


located at the other end of the subsidiary rod


68


, are clearance-fitted into the bifurcation


72


located at the other end. Moreover, a pair of clips


77


,


77


are mounted to the bifurcation


72


located at the other end, to thereby abut against opposite ends of the subsidiary rod pin


76


and inhibit the disengagement of the subsidiary rod pin


76


from the bifurcation


72


.




Further, the crank cap


73


is fastened to the bifurcations


71


and


72


by pair of bolts


78


disposed on opposite sides of the crankshaft


27


. The connecting rod pin


75


and the subsidiary rod pin


76


are disposed on extensions of axes of the bolts


78


.




The cylindrical eccentric shaft


61


is integrally provided at an eccentric location on a support shaft


81


turnably carried in the crankcase


22


of the engine body


21


and having an axis parallel to the crankshaft


27


. The support shaft


81


is turnably carried at one end on a bottomed cylindrical bearing housing


82


provided on the side cover


26


of the crankcase


22


with a ball bearing


83


interposed therebetween. The other end of the support shaft


81


is turnably passed through the case body


25


of the crankcase


22


, and a ball bearing


84


is interposed between the case body


25


and the support shaft


81


.




A one-way clutch


85


is mounted between the bearing housing


82


and the support shaft


81


outside the ball bearing


83


. An annular seal member


86


is interposed between the case body


25


and the support shaft


81


outside the ball bearing


84


.




A load in a direction to compress the control rod


69


and a load in a direction to expand the control rod


69


, are alternately applied to the control rod


69


connected at the other end to the eccentric shaft


61


, depending on the operational cycle of the engine. A rotational force toward one side and a rotational force toward the other side, are also applied from the control rod


69


to the support shaft


81


, because the eccentric shaft


61


is provided at the eccentric location on the support shaft


81


. That is, the support shaft


81


is capable of turning only in one direction shown by an arrow


80


in

FIG. 4

, because the one-way clutch


85


is interposed between the support shaft


81


and the bearing housing


82


on the side cover


26


of the crankcase


22


.




Referring also to

FIG. 5

, a small-diameter shaft portion


81




a


is coaxially provided on the support shaft


81


at a location axially spaced apart from the eccentric shaft


61


in such a manner that an annular recess


81




b


is formed around an outer periphery of the small-diameter shaft portion


81




a


. Limiting abutments


87


and


88


are integrally provided on the small-diameter shaft portion


81




a


at a plurality of, e.g., two points axially spaced apart from each other, with their positions displaced from each other in a circumferential direction of the support shaft


81


.




Then turned position of the support shaft


81


is limited to a plurality of points, e.g., two points by a turned-position limiting means


89


. The turned-position limiting means


89


comprises a turn shaft


90


turnably carried in the crankcase


22


and having an axis perpendicular to an axis of the support shaft


81


, and a limiting member


91


fixed to the turn shaft


90


, so that the limiting member


91


can be put into abutment alternatively against the limiting abutments


87


,


88


by the rotation of the turn shaft


90


.




A bottomed cylindrical shaft-supporting portion


92


and an annular shaft-supporting portion


93


are integrally provided on the case body


25


of the crankcase


22


, so that they are opposed to each other at a distance on the same axis perpendicular to the axis of the support shaft


81


. The turn shaft


90


having one end disposed adjacent the shaft-supporting portion


92


is turnably carried on the shaft-supporting portions


92


and


93


, with the other end protruding outwards from the shaft-supporting portion


93


.




The limiting member


91


is fixed by a pin


94


to the turn shaft


90


between the shaft-supporting portions


92


and


93


, and is integrally provided with a projection


91




a


which is capable of protruding into the annular recess


81




b


to abut alternatively against the limiting abutments


87


and


88


.




The support shaft


81


is turned by the application of a load on the control rod


69


which is connected to the eccentric shaft


61


mounted in the eccentric position on the support shaft


81


, when a state in which the projection


91




a


of the limiting member


91


is in abutment against one of the limiting abutments


87


and


88


and a state in which the projection


91




a


is in abutment against the other of the limiting abutments


87


and


88


are switched over from one to the other. However, it is necessary to avoid that one of the limiting abutments


87


and


88


is put into abutment with a shock against the projection


91




a


of the limiting member


91


by the turning of the support shaft


81


. Therefore, a thrust moderating means


97


for moderating the shock in an axial direction upon the abutment of the limiting abutment


87


or


88


against the alternatively selected limiting member


91


, is interposed between the shaft-supporting portion


93


of the crankcase


22


and the limiting member


91


.




The thrust moderating means


97


includes a ring-shaped rubber member


99


clamped between a pair of washers


98


,


98


, through which the turn shaft


90


is passed. The rubber member


99


has a high hardness, an oil resistance and a heat resistance, and moreover is baked to the washers


98


,


98


.




Referring also to

FIG. 6

, a diaphragm-type actuator


101


is connected to the turn shaft


90


of the turned-position limiting means


89


. The actuator


101


includes: a casing


103


mounted to a support plate


102


fastened to an upper portion of the case body


25


of the crankcase


22


; a diaphragm


106


supported in the casing


103


to partition the inside of the casing


103


into a negative pressure chamber


104


and an atmospheric pressure chamber


105


; a spring


107


mounted under compression between the casing


103


and the diaphragm


106


to exhibit a spring force in a direction to increase the volume of the negative pressure chamber


104


; and an actuating rod


108


connected to a central portion of the diaphragm


106


.




The casing


103


comprises a first bowl-shaped case half


109


mounted to the support plate


102


, and a second bowl-shaped case half


110


bonded by crimping to the case half


109


. A peripheral edge of the diaphragm


106


is clamped between opening edges of the case halves


109


and


110


. The negative pressure chamber


104


is defined between the diaphragm


106


and the second case half


110


, and accommodates therein a spring


107


.




The atmospheric chamber


105


is defined between the diaphragm


106


and the first case half


109


. The actuating rod


108


passed through a through-bore


111


which is provided in a central portion of the first case half


109


to protrude into the atmospheric pressure chamber


105


, is connected at one end to a central portion of the diaphragm


106


. The atmospheric pressure chamber


105


communicates with the outside through a clearance between an inner periphery of the through-bore


111


and an outer periphery of the actuating rod


108


.




A conduit


112


leading to the negative pressure chamber


104


is connected to the second case half


110


of the casing


103


, and also connected to a downstream end of the intake passage


46


in the carburetor


35


. Namely, an intake negative pressure in the intake passage


46


is introduced into the negative pressure chamber


104


in the actuator


101


.




The other end of the actuating rod


108


of the actuator


101


is connected to a driving arm


113


carried on the support plate


102


for turning about an axis parallel to the turn shaft


90


. A driven arm


114


is fixed to the other end of the turn shaft


90


protruding from the crankcase


22


. The driving arm


113


and a driven arm


114


are connected to each other through a connecting rod


115


. A spring


116


is mounted between the driven arm


114


and the support plate


102


, to urge the driven arm


114


to turn it in a clockwise direction in FIG.


6


.




When the engine is in a light-load operational state in which the negative pressure in the negative pressure chamber


104


is high, the diaphragm


106


is flexed to decrease the volume of the negative pressure chamber


104


against spring forces of the return spring


107


and the spring


116


, and the actuating rod


108


is contracted, as shown in FIG.


6


. In this state, the turned positions of the turn shaft


90


and the limiting member


91


of the turned-position limiting means


89


are positions at which the projection


91




a


of the limiting member


91


is in abutting engagement with one


87


of the limiting abutments


87


and


88


of the support shaft


81


.




On the other hand, when the engine is brought into a high-load operational state in which the negative pressure in the negative pressure chamber


104


is low, the diaphragm


106


is flexed to increase the volume of the negative pressure chamber


104


by the spring forces of the return spring


107


and the spring


117


, and the actuating rod


108


is expanded, as shown in FIG.


7


. Thus, the turn shaft


90


and the limiting member


91


of the turned-position limiting means


89


are turned to the positions at which the projection


91




a


of the limiting member


91


is in abutting engagement with one


88


of the limiting abutments


87


and


88


of the support shaft


81


.




As described above, the turning of the support shaft


81


, to which the rotational force is applied in one direction during operation of the engine, is restricted to the position at which any one of the limiting abutments


87


,


88


is in engagement with the projection


91




a


of the limiting member


91


by turning the limiting member


91


. The eccentric shaft


61


which is in the position eccentric from the axis of the support shaft


81


, i.e., the other end of control rod


69


, is displaced between two positions in a plane perpendicular to the axis of the crankshaft


27


by stopping the turning of the support shaft


81


in each of two positions with phases different from each other, for example, by 167 degrees, whereby the compression ratio of the engine is changed.




Referring to

FIGS. 8 and 9

, in order to avoid that the limiting abutments


87


and


88


are put into abutment with a shock alternatively against the projection


91




a


of the limiting member


91


by the turning of the support shaft


81


when the compression ratio is changed, a radial buffer means


120


for moderating a load in a radial direction applied from the control rod


69


to the support shaft


81


is mounted between one end of the support shaft


81


and the bearing housing


82


of the crankcase


22


on the engine body


21


.




The radial buffer means


120


includes: an eccentric cam


121


integrally provided on the support shaft


81


so that it is located adjacent the small-diameter shaft portion


81




a


on the side of the ball bearing


83


; a spring holder


122


engaged with the bearing housing


82


to surround the eccentric cam


121


so that the spring holder


122


is prevented from turning about the axis of the support shaft


81


; and a compression spring


123


retained on the holder


122


to come into friction contact with the eccentric cam


121


.




A cylindrical portion


124


is provided coaxially on the support shaft


81


to surround the eccentric cam


121


. The spring holder


122


is slidably fitted into the cylindrical portion


124


. A ring-shaped support plate


125


opposed to the ball bearing


83


and the bearing housing


82


is integrally connected to the spring holder


122


. An annular projection


126


is provided integrally and projectingly at an end of the support plate


125


closer to the bearing housing


82


, so that an annular groove, into which a tip end of the cylindrical portion


124


is inserted, is formed between the projection


126


and the spring holder


122


, and an engagement plate portion


127


is provided integrally on the bearing housing


82


at circumferential one point to protrude radially outwards.




The engagement plate portion


127


is clamped between a pair of locking plate portions


128


,


128


projectingly provided on a tip end face of the bearing housing


82


, whereby the rotation of the spring holder


122


about the axis of the support shaft


81


is inhibited. Moreover, an annular abutment


129


is provided integrally and projectingly on the support plate


125


and supported in an abutting manner on an outer race


83




a


of the ball bearing


83


.




The compression spring


123


is formed into a substantially endless shape and has a split groove


130


at circumferential one point, and is formed with engagement portions


123




a


and


123




b


which are bulged radially outwards in a trapezoidal shape to come into engagement in a pair of engagement bores


131


,


131


provided in the spring holder


122


on one diametrical line of the support shaft


81


, and a pair of flexible abutments


123




c


and


123




d


flexed radially to be able to come resiliently into sliding contact with the eccentric cam


121


. The flexible abutments


123




c


and


123




d


are disposed at two points on a straight line perpendicular to a line connecting the engagement portion


123




a


and


123




b


to each other.




With the radial buffer means


120


, the eccentric cam


121


turns one of the flexing abutments


123




c


and


123




d


, while flexing it, during turning of the support shaft


81


, so that the radial load applied from the control rod


69


to the support shaft


81


upon the change of the compression ratio can be moderated. Moreover, the combustion in the engine is utilized when the compression ratio is changed from a lower compression ratio to a higher compression ratio, leading to a possibility that a larger shock is applied to the support shaft


81


. Therefore, the amount of initial deformation of one


123




c


of the flexible abutments


123




c


and


123




d


which is brought into contact with the eccentric cam


121


during the changing of the compression ratio from the lower compression ratio to the higher compression ratio, is set larger than that of the flexible abutment


123




d


. Thus, the shock applied to the support shaft


81


during the changing of the compression ratio from the lower compression ratio to the higher compression ratio can be effectively moderated, so that it is possible to avoid that an unnecessary turning resistant torque is applied to the support shaft


81


during the changing of the compression ratio from the higher compression ratio to the lower compression ratio.




Referring again to

FIG. 2

, a case


134


of a recoil starter


34


comprises a case member


135


formed into a cylindrical shape to surround the flywheel


32


and fastened to the case body


25


of the crankcase


22


, and a cap-shaped case member


136


fastened to the case member


135


to close an open end of the case member


135


. A reel


138


is rotatably carried on a shaft


137


mounted in the case member


136


coaxially with the crankshaft


27


, and a spiral spring


139


is mounted between the shaft


137


and the reel


138


.




One end of a rope


140


wound around the reel


138


is tied at one end to the reel


138


, and the other end of the rope


140


is drawn to the outside from an opening


141


provided in the case member


136


.




A portion of the reel


138


is covered with a cap-shaped starter pulley


142


secured to one end of the crankshaft


27


, and a ratchet


144


is carried on the reel


138


and capable of being engaged into a locking recess


143


provided in an inner periphery of the starter pulley


142


.




Thus, when the rope


140


is pulled against a spring force of the spiral spring


139


and a pulling force is then released, the reel


138


is rotated by the spring force of the spiral spring


139


, and the ratchet


144


is brought into engagement in the locking recess


143


in the starter pulley


142


, whereby a starting rotational power is transmitted from the reel


138


to the crankshaft


27


.




Referring to

FIGS. 10 and 11

, a buffering/accumulating means


145


is disposed between the case body


25


of the crankcase


22


and the flywheel


32


, so that a rotational force in the same direction as that of the recoil starter


34


can be transmitted to the flywheel


32


.




The buffering/accumulating means


145


includes a spiral spring


148


mounted between an output member


146


and an input member


147


disposed coaxially with the crankshaft


27


. The output member


146


and the input member


147


each formed into a ring plate-shape to coaxially surround the crankshaft


27


, are disposed at a distance from each other in an axial direction of the crankcase


27


with the output member


146


positioned at a location closer to the crankcase


22


.




A substantially cylindrical outer tube


149


extending coaxially with the crankshaft


27


at a location corresponding to an outer periphery of the input member


147


is secured at one end to the output member


146


. The intake member


147


is integrally formed with an inner tube


150


which is disposed coaxially with the crankshaft


27


inside the outer tube


149


. The spiral spring


148


is accommodated in a space defined by the output member


136


, the outer tube


149


, the input member


147


and the inner tube


150


, and connected at opposite ends in an engaging manner to the outer tube


149


and the inner tube


150


.




In such buffering/accumulating means


145


, the spiral spring


148


can be wound up for accumulation of power by rotating the input member


147


in a state in which the output member


146


is restrained for inhibition of the rotation thereof. If the restraint of the output member


146


is releaed while inhibiting the rotation of the input member


147


, the output member


146


is rotated by an accumulated spring force of the spiral spring


148


.




In order to transmit such a rotational power of the output member


146


to the flywheel


32


, trapezoidal locking projections


151


,


151


which protrudes radially inwards are integrally provided on an inner periphery of the flywheel


32


at a plurality of, e.g., two points circumferentially spaced at equal distances apart from each other. On the other hand, recesses


152


,


152


depressed radially inwards are provided in the outer tube


149


secured to the output member


146


at a plurality of, e.g., two points circumferentially spaced at equal distances apart from each other. Ratchets


153


,


153


are carried on the output member


146


to come into engagement with the locking projections


151


,


151


for turning between positions in which they protrude outwards from the recesses


152


,


152


and positions in which they are accommodated in the recesses


152


,


152


. Namely, the ratchets


153


,


153


are integrally provided with shafts


154


,


154


which are parallel to the crankshaft


27


and which are turnably carried on the output member


146


.




Moreover, each of rollers


155


,


155


is secured coaxially to one end of each of the shafts


154


,


154


at a point protruding from the output member


146


toward the case body


25


of the crankcase


22


. A cylindrical guide tube


156


is provided integrally and projectingly on the case body


25


, so that the rollers


155


,


155


are rolled on the cylindrical guide tube


156


.




Thus, when the output member


146


is rotated in a direction shown by an arrow


157


in

FIG. 11

, the rollers


155


,


155


are rolled along an inner surface of the guide tube


156


, whereby the shafts


154


,


154


are turned in a direction so that the ratchets


153


,


153


protrude from the recesses


152


,


152


. The ratchets


153


,


153


protruding from the recesses


152


,


152


are brought into engagement with the locking projections


151


,


151


, respectively, thereby permitting the rotational power of the output member


146


to be transmitted to the flywheel


32


.




A transmitting tube


158


disposed coaxially with the crankshaft


27


inside the inner tube


150


is fixed to an inner peripheral portion of the input member


147


by a plurality of rivets


159


, and rotatably carried on the case body


25


of the crankcase


22


with a ball bearing


160


interposed therebetween. A cylindrical support tube


161


is integrally formed on an inner periphery of the output member


146


to come into sliding contact with an outer periphery of the transmitting tube


158


.




A rotational torque in a direction to wind up the spiral spring


148


is transmitted from the support shaft


81


through a torque transmitting means


162


and the transmitting tube


158


to the input member


147


of the buffering/accumulating means


145


.




Referring to

FIGS. 12 and 13

, the torque transmitting means


162


is constructed so that it transmits the rotational torque in the direction to wind up the spiral spring


148


until the completion of the winding-up of the spiral spring


148


, but it enables the support shaft


81


to be raced after the completion of the winding-up of the spiral spring


148


. The torque transmitting means


162


includes: a ring member


163


surrounding the support shaft


81


at a portion protruding from the case body


25


of the crankcase


22


; a pair of balls


164


,


164


capable of being switched over between a state in which both of them are in engagement with the support shaft


81


and the ring member


163


and a state in which they are out of engagement with the ring member


163


and retained on the support shaft


81


; a spring


165


mounted between the balls


164


,


164


to exhibit a spring force for biasing the balls


164


,


164


in directions to bring them into engagement with the support shaft


81


and the ring member


163


; a driving gear


166


integrally provided on an outer periphery of the ring member


163


; and a driven gear


167


integrally provided on the transmitting tube


158


to become meshed with the driving gear


166


.




The ring member


163


surrounds the support shaft


81


with its axial position determined constant. A through-bore


158


is provided in the support shaft


81


at a location corresponding to the ring member


163


, and extends along one diametrical line. On the other hand, an annular groove


169


and a pair of locking recesses


170


,


170


are provided in an inner periphery of the ring member


163


. The locking recesses


170


,


170


are formed so that they are depressed outwards from the annular groove


169


on one diametrical line of the ring member


163


.




A portion of each of the balls


164


,


164


is inserted into each of opposite ends of the through-bore


169


. The spring


165


is accommodated in the through-bore


169


, so that it is interposed between the balls


164


,


164


. The annular groove


169


is formed to have a depth enough to roll the balls


164


,


164


accommodated by half in the opposite ends of the through-bore


169


. The locking recesses


170


,


170


are formed into semi-circular shapes in such a manner that the balls


164


,


164


accommodated substantially by half in the opposite ends of the through-bore


169


are engaged therein.




In such torque transmitting means


162


, the rotational torque of the support shaft


81


is transmitted to the input member


147


through the ring member


163


, the driving gear


166


, the driven gear


167


and the transmitting tube


158


, by the turning of the support shaft


81


in a state in which the balls


164


,


164


are engagement in the locking recesses


170


,


170


, i.e., in a state in which the balls


164


,


164


are in engagement with the support shaft


81


and the ring member


163


. Therefore, in the buffering/accumulating means


145


which is in a state in which the rotation of the output member


146


is inhibited, the spiral spring


148


is wound up.




Moreover, the spring force of the spiral spring


148


serves as a resistance, and the radial load applied from the control rod


69


to the support shaft


81


upon the changing of the compression ratio can be moderated, so that the torque transmitting means


162


also functions as a radial buffering means.




After the completion of the winding-up of the spiral spring


148


, when support shaft


81


is turned upon the changing of the compression ratio, the support shaft


81


is raced to repeat the state in which the balls


164


,


164


are in engagement in the locking recesses


170


,


170


and a state in which the balls


164


,


164


are rolled in the annular groove


169


. The radial load applied from the control rod


69


to the support shaft


81


upon the changing of the compression ratio can be moderated by a resisting force generated when the balls


164


,


164


climbs over the locking recesses


170


,


170


into the annular groove


169


against the spring force of the spring


165


. Therefore, even in this case, the torque transmitting means


162


also functions as the radial buffering means.




In the present embodiment, a notch


156




a


is provided in the guide tube


156


at a location corresponding to the torque transmitting means


162


for avoiding the interference of the guide tube


156


with the torque transmitting means


162


.




The rotation of the output shaft


146


of the buffering/accumulating mans


145


is limited by an accumulation releasing/restricting means


171


. The accumulation releasing/restricting means


171


inhibits the rotation of the output member


146


during non-operation of the recoil starter


34


, but permits the rotation of the output member


146


upon the starting operation of the recoil starter


34


.




Referring also to

FIG. 14

, the accumulation releasing/restricting means


171


includes a limiting step


172


provided around an outer periphery of the output member


146


to face a downstream in a rotational direction shown by an arrow


157


in

FIG. 11

, a limiting rod


173


extending in parallel to the crankshaft


27


to inhibit the rotation of the output member


146


by the engagement with the limiting step


172


with its one end being in engagement in an engagement bore


174


provided in the case body


25


of the crankcase


22


, a swinging arm


175


which is swingably carried on a support member


176


fixed to the case member


135


of the case


134


of the recoil starter


34


, and one end of which is engaged with the other end of the limiting rod


173


, and a return spring


177


mounted between the case member


135


and the swinging arm


175


to exhibit a spring force for biasing the limiting rod


173


in a direction to bring one end of the limiting rod


173


into engagement in the engagement bore


174


.




The support member


176


is secured to an inner surface of the case member


135


in the vicinity of the opening


141


, and has an insertion bore through which the rope


140


of the recoil starter


32


passes. The swinging arm


175


formed to sandwich the support member


176


from opposite sides is swingably carried at its intermediate portion on the support member


176


through a shaft


179


perpendicular to the limiting rod


173


. The return spring


177


is a torsion spring, and is mounted between the case member


135


and the swinging arm


175


to surround the shaft


179


.




In a state in which the recoil starter


34


is not operated, the swinging arm


175


has been turned by a spring force of the return spring


177


to a position at which the rope


140


is sandwiched between the other end of the swinging arm


175


and the support member


176


. In this state, the limiting rod


173


which is at a position with end thereof being engaged in the engagement bore


174


, is in engagement with the limiting step


172


to inhibit the rotation of the output member


176


.




When the rope


140


of the recoil starter


34


is pulled to start the engine in such state, an urging force is applied from the rope


140


to the other end of the swinging arm


175


by tightening of the rope


140


, whereby the swinging arm


175


is turned against the spring force of the return spring


177


, so that the limiting rod


173


is engaged from the engagement bore


174


. Thus, one end of the limiting rod


173


is brought into a free state, and the limiting rod


173


is brought into a state in which it is swingably supported at the other end on the swinging arm


175


. Therefore, the output member


146


is brought into a state in which the rotation thereof is permitted, so that when the spiral spring


148


retains accumulated force, the output member


146


is rotated.




The operation of the present embodiment will be described below. The direction of turning of the support shaft


81


having the eccentric shaft


61


in the eccentric position, to which the control rod


69


has been connected, is limited to one direction by the one-way clutch


85


mounted between the side cover


26


of the crankcase


22


in the engine body


21


and the support shaft


81


, and an expansion load and a compressing load are applied to the control rod


69


by the combustion in the engine and inertia. Therefore, when the compression ratio is changed, the support shaft


81


and the eccentric shaft


61


are turned in the direction limited by the one-way clutch


85


.




The turned position of the support shaft


81


is limited selectively at a plurality of, e.g., two positions by the turned-position limiting means


89


, and the compression ratio of the engine is changed by changing the turned position of the support shaft


81


.




Moreover, the rotational force is transmitted from the recoil starter


34


to the flywheel


32


secured to the crankshaft


27


in response to the starting operation of the engine. The rotational torque in the same direction as that of the recoil starter


34


can be transmitted to the flywheel


32


from the buffering/accumulating means


145


including the spiral spring


148


mounted between the output member


146


and the input member


147


disposed coaxially with the crankshaft


27


. The torque transmitting means


162


, which is capable of transmitting the rotational torque in the direction to wind up the spiral spring


148


from the support shaft


81


to the input member


146


until the completion of the winding-up of the spiral spring


148


, but permitting the support shaft


81


to be raced after the completion of the winding-up of the spiral spring


148


, is mounted between the support shaft


81


and the input member


146


. The rotation of the output member


146


of the buffering/accumulating means


145


is inhibited by the accumulation releasing/restricting means


171


when the recoil starter is not operated, and the accumulation releasing/restricting means


171


permits the rotation of the output member


146


in response to the starting operation of the recoil starter


34


.




Therefore, when the compression ratio is changed over, the rotational torque of the support shaft


81


is transmitted through the torque transmitting means


162


to the input member


147


of the buffering/accumulating means


145


. Thus, the force can be accumulated in the spiral spring


148


by the winding-up of the spiral spring


148


, and the load applied to the support shaft


81


can be absorbed by the spiral spring


148


, thereby contributing to the moderation of the shock. Namely, while the support shaft


81


is turned to a next turning-limited position by the turned-position limiting means


89


upon the change-over of the compression ratio, the rotational torque applied to the support shaft


81


can be accumulated by the spiral spring


148


of the buffering/accumulating means


145


. During the accumulation of the force in the spiral spring


148


, the rotation of the output member


146


is inhibited by the accumulation releasing/restricting means


171


, but when the recoil starter


34


is started at the next start of the engine, the accumulation releasing/restricting means


171


permits the rotation of the output member


146


. Therefore, the spring force accumulated in the spiral spring


148


is transmitted from the output member


146


to the flywheel


32


, so that even if the pulling load on the recoil starter


34


is alleviated, the engine can be started sufficiently.




The turning-limiting means


89


is adapted to abut alternatively against the limiting abutments


87


,


88


provided on the support shaft


81


with their positions circumferentially displaced from each other, to thereby limit the turned position of the support shaft


81


. The turning-limiting means


89


has the limiting member


91


which is carried on the case body


25


of the crankcase


22


on the engine body


21


and which is capable of turning about the axis perpendicular to the support shaft


81


. The actuator


101


for driving the limiting member


91


to turn is connected to the limiting member


91


. The thrust buffering means


97


for moderating the shock in the axial direction upon the abutment of the limiting abutment


87


or


88


against the alternatively selected limiting member


91


is interposed between the limiting member


91


and the shaft-supporting portion


93


of the case body


25


.




When one of the limiting abutments


87


and


88


and the limiting member


91


are brought into contact with each other, a shock is applied to the limiting member


91


in a direction perpendicular to the axis of the support shaft


81


, but such a shock can be moderated by a simple construction in which the thrust buffering means


97


is interposed between the limiting member


91


and the shaft-supporting portion


93


of the case body


25


. Thus, it is possible to avoid the application of the shock to the actuator


101


for driving the limiting member


91


and to enhance the durability reliability, while avoiding the increases in sizes of various members such as the support shaft


81


and the limiting member


91


due to the increasing of their strengths. Moreover, it is also possible to suppress to a low level a sound generated when one of the limiting abutments


87


and


88


and the limiting member


91


are brought into contact with each other.




The radial buffering means


120


for moderating the radial load applied from the control rod


69


to the support shaft


81


is mounted between the support shaft


81


and the side cover


26


of the crankcase


22


on the engine body


21


. The torque transmitting means


162


also functioning as the radial buffering means is mounted between the buffering/accumulating means


145


and the support shaft


81


.




Therefore, when the compression ratio is changed over, even if a large load is applied to the support shaft


81


and the turned-position limiting means


89


, the radial load applied to the support shaft


81


is moderated by the radial load buffering means


120


and the torque transmitting means


162


. Thus, it is possible to enhance the durability reliability, while avoiding the increases in sizes of various members such as the support shaft


81


and the turned-position limiting means


89


due to the increasing of their strengths. Moreover, it is possible to suppress to a low level a sound generated when the turned position is limited by the turned-position limiting means


89


.




Although the embodiment of the present invention has been described in detail, it will be understood that the present invention is not limited to the above-described embodiment, and various modifications in design may be made without departing from the spirit and scope of the invention defined in the claims.



Claims
  • 1. An engine of a compression-ratio variable type, comprising a connecting rod connected at one end to a piston through a piston pin, a subsidiary rod connected to a crankshaft through a crankpin and to the other end of said connecting rod, a control rod connected at one end to said subsidiary rod at a location displaced from a connected position of said connecting rod, a support shaft turnably carried in an engine body, and an eccentric shaft mounted at an eccentric location on said support shaft and connected to the other end of said control rod, the turned position of the support shaft being changed to change the compression ratio,wherein the engine further includes a one-way clutch mounted between said support shaft and said engine body in such a manner that the direction of turning of said support shaft is limited, a turned-position limiting means for limiting the turned position of said support shaft selectively at a plurality of points, and buffering means for moderating a load applied to at least one of said support shaft and said turned-position limiting means upon changing-over of said compression ratio.
  • 2. An engine of a compression-ratio variable type according to claim 1, wherein a flywheel is secured to said crankshaft so that a rotational force is transmitted from a recoil starter to said flywheel in response to the starting operation of the engine; said buffering means comprises an output member disposed coaxially with said crankshaft in such a manner that the rotational force in the same direction as that of said recoil starter can be transmitted to said flywheel, and the rotation thereof is limited when said recoil starter is not operated, an input member coaxial with said output member, and a spiral spring mounted between said output member and said input member; and a torque transmitting means is mounted between said support shaft and said input member so that it transmits the rotational force in a direction to wind up the spiral spring from said support shaft to said input member until the completion of the winding-up of said spiral spring, but it permits said support shaft to be raced after the completion of the winding-up of said spiral spring.
  • 3. An engine of a compression-ratio variable type according to claim 1, wherein limiting abutments are provided on said support shaft at a plurality of points axially spaced apart from each other with their positions displaced in a circumferential direction of said support shaft; an actuator is connected to a limiting member for driving said limiting member in turning, said limiting member being carried in the engine body to constitute a portion of said turned-position limiting means so that it can be turned about an axis perpendicular to said support shaft to come into abutment alternatively against one of said limiting abutments to limit the turned position of said support shaft; and said buffering means is interposed between said limiting member and the engine body in order to moderate an axial shock upon the abutment of the alternatively selected limiting abutment against said limiting member.
  • 4. An engine of a compression-ratio variable type according to claim 1, wherein said buffering means is mounted between said support shaft and the engine body to moderate the radial load applied from said control rod to said support shaft.
Priority Claims (3)
Number Date Country Kind
2002-313706 Oct 2002 JP
2002-313707 Oct 2002 JP
2002-313708 Oct 2002 JP
Foreign Referenced Citations (4)
Number Date Country
42 26 361 Apr 1994 DE
321684 Nov 1929 GB
9-228858 Feb 1997 JP
2002276446 Sep 2002 JP