Valve system for engine

Information

  • Patent Grant
  • 6789521
  • Patent Number
    6,789,521
  • Date Filed
    Friday, April 5, 2002
    23 years ago
  • Date Issued
    Tuesday, September 14, 2004
    20 years ago
Abstract
A decompression system for a four-cycle engine includes a decompression shaft positioned within a camshaft. The decompression shaft interacts with decompression pins positioned within pin holes formed in the camshaft. In some embodiments, the decompression shaft is formed from a first longitudinal portion and a second longitudinal portion. In other embodiments, the decompression shaft is supported at least in part by a middle portion of a bore that extends through the camshaft.
Description




BACKGROUND OF THE INVENTION




1. Field of the Invention




This invention relates generally to a valve system of a four cycle engine and more particularly to an engine decompression system for the valve system.




2. Description of the Related Art




Many four cycle engines include a decompression system to make starting the engine easier. Such decompression systems are desired because of the high compression ratios that are often used in four-cycle engines. The high compression ratios produce large compression forces that must be overcome by an operator or a starter motor to start the engine. The decompression system reduces these forces by opening the exhaust valves and thereby effectively reducing the compression ratio when starting the engine.




There are several types of decompression systems. See, e.g., U.S. Pat. Nos. 4,369,741, 5,816,208 and 6,343,579. In U.S. Pat. No. 5,816,208, the decompression system includes a decompression actuating shaft that is inserted into a bore formed within a camshaft. The decompression actuating shaft actuates pins that are moveably positioned within pinholes positioned within the camshaft. When actuated by the decompression actuating shaft, the pins lift the exhaust valves to reduce the compression ration.




SUMMARY OF THE INVENTION




A need exists for an improved decompression system that is easy to manufacture and assemble and is also reliable. In particular, in engines with multiple cylinders (e.g., three or more), the camshaft and decompression actuating shaft become increasingly long. This tends to increase the difficult and costs of manufacture and assembly and to reduce reliability.




In one embodiment of the present invention, a decompression system for a four-cycle engine comprises a camshaft, decompression shaft, and at least one decompression pin. The camshaft has at least one cam arranged to activate a valve of the engine and an internal bore that extends generally longitudinally with respect to the camshaft. The camshaft also includes at least one pin hole arranged generally perpendicular to the internal bore. The decompression shaft comprises a first longitudinal portion and a second longitudinal portion that are configured to fit within the internal bore of the camshaft. The decompression shaft is moveable between a first position and a second position and further comprises at least one cam surface having a first portion and a second portion. The cam surface is arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve.




In another aspect of the present invention, a method of assembling a decompression system for an engine comprising forming a bore within the camshaft, the bore having a middle portion with a first diameter and a second portion with a second diameter that is larger than the first diameter, forming at least one pin hole in the camshaft, the pin hole extending generally perpendicular to a longitudinal axis of the camshaft, inserting a pin into the pin hole, forming a first portion of a decompression shaft, forming a second portion of a decompression shaft, and inserting the first portion and second portions of the decompression shaft into the bore.




All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment(s) disclosed.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic top plan view of a cylinder head of a four cylinder, four-cycle engine having an exhaust camshaft and a decompression system with certain features and advantages according to a preferred embodiment of the present invention.





FIG. 2A

is a cross-sectional view of the exhaust camshaft of FIG.


1


and illustrates the decompression system in a non-activated position.





FIG. 2B

is a cross-sectional view of the exhaust camshaft of FIG.


1


and illustrates the decompression system in an activated position.





FIG. 3

is an enlarged view of one end of the decompression system as seen in the direction of arrow


3


in FIG.


1


.





FIG. 4

is an enlarged view of a drive apparatus of the decompression system as seen in the direction of arrows


4





4


in FIG.


1


.





FIG. 5

is an enlarged view of the drive apparatus of the decompression system as seen in the direction of arrows


5





5


in FIG.


1


.





FIG. 6A

is an enlarged cross-sectional view of a portion of the exhaust camshaft the decompression shaft of

FIG. 2A

, showing the decompression system in a non-activated position.





FIG. 6B

is an enlarged cross-sectional view of a portion of the exhaust camshaft the decompression shaft of

FIG. 2B

, showing the decompression system in an activated position.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT





FIGS. 1-6B

illustrate a valve system


10


of a four-cycle engine. The valve system includes an exhaust camshaft


12


, an intake camshaft


14


and a decompression system


16


having certain features and advantages of the present invention. Because the present invention deals primarily with the configuration of the valve system and the decompression system, only the portions of an engine that form or directly cooperate with the valve and decompression systems


10


,


16


are illustrated in the figures. The remaining elements of the engine that are not illustrated or described in detail may be considered to be conventional and are well known to those of ordinary skill in the art.




With initial reference to

FIG. 1

, the exhaust and intake camshafts


12


,


14


are shown positioned within the cylinder head


18


of the engine in a “dual overhead” arrangement. In the illustrated arrangement, the engine includes four cylinders with three intake valves and two exhaust valves associated with each cylinder. As such, the intake camshaft includes three intake cams


20


for each cylinder (i.e., twelve total) and the exhaust camshaft includes two exhaust cams


22


for each cylinder (i.e., eight total). Those of skill in the art will recognize the illustrated engine as an in-line, four cycle, four-cylinder engine. However, it should be appreciated that several features and advantages of the present invention may be achieved in an engine having a different arrangement (e.g., V-type), more or less cylinders, more or less intake and exhaust valves and operating on a different combustion principle (e.g., two-cycle or compression).




The intake cams


20


open and close intake valves as is well known in the art. The intake valves control the flow of an intake charge into the combustion chamber. In the illustrated embodiment, the intake charge is delivered to the combustion chambers through intake passages that are formed in the cylinder head


18


and are connected to an induction system through a series of intake pipes


24


. In a similar manner, the exhaust cams


22


open and close exhaust valves


26


(see FIGS.


2


A and


5


). In the illustrated embodiment, the exhaust valves


26


(as well as the intake valves) include compression springs


28


for biasing the valves


26


to a closed position and a bearing surface


30


of a tappet


31


for contacting the exhaust cams


22


and intake cams


20


respectively. The exhaust is expelled from the combustion chamber through an exhaust passage


32


(see

FIG. 5

) that is formed in the cylinder head


18


and is connected to a series of exhaust pipes


34


.




The camshafts


12


,


14


are suitably journalled for rotation within the cylinder head


18


by a series of bearings as is well known in the art. The camshafts


12


,


14


are preferably driven by the engine's crankshaft by a flexible transmitter (e.g.,. a timing belt) at one half the crankshaft speed.




The decompression system


16


will now be described with initial reference to

FIGS. 2A and 2B

. The decompression system


16


includes a decompression shaft


34


, which in the illustrated embodiment comprises a first portion


36


A and a second portion


36


B. The first and second portions are coupled together at a coupling point


38


that is preferably located near the center of the exhaust camshaft


12


.




The exhaust camshaft


12


includes a bore


40


in which the decompression shaft


34


is positioned. In the illustrated embodiment, the bore


40


extends completely through the exhaust cam shaft


12


. However, in modified arrangements, the bore


40


can have only one opening and/or extend only partially through the exhaust camshaft


12


. Preferably, the bore


40


is formed such that the decompression shaft


34


and the exhaust camshaft


12


have the same longitudinal axis


41


.




The areas of the exhaust camshaft


12


near or adjacent at least one of the exhaust cams


22


associated with each cylinder include a pin hole


42


. Within each pin hole


42


, there is provided a decompression pin


44


. The pin holes


42


are arranged such that the decompression pins


44


are generally aligned with a bearing surface


30


of the tappet


31


of one of the exhaust valves


26


as will be explained in more detail below. Each pin hole


42


is generally perpendicular to the longitudinal axis


41


of the exhaust camshaft


12


and each decompression pin


44


is biased by a biasing member (e.g., a coil spring) such that the decompression pin is biased towards the longitudinal axis


41


(i.e., the center of the bore


40


).




In the illustrated arrangement, the decompression system


16


includes three decompression pins


44


positioned within three pin holes


42


. Each decompression pin is aligned with one of the two exhaust valves


26


that is associated with each cylinder. However, it should be appreciated that in modified embodiments, the decompression system


16


can include more or less pin holes


42


and decompression pins


44


that are arranged for actuating more or less of the exhaust vales


26


. Moreover, in still other embodiments, the pin holes


42


and decompression pins


44


may be arranged for actuating the exhaust valves


26


of only some of the cylinders.




As mentioned above, the bore


40


is preferably open at both ends of the exhaust camshaft


12


. In addition, the bore


40


preferably includes a larger diameter portion


46


A,


46


B at both open ends and smaller diameter first middle portions


46


C between the larger diameter portions. The coupling point


38


of the decompression shaft


34


is preferably located within a second middle portion


46


D near the center of the camshaft


12


between the first middle portions


46


C. The second middle portion


46


D of the bore


40


forms a bearing surface


48


, which is also indicated by the shaded area


50


of

FIGS. 2A and 2B

. The second diameter portion


46


D preferably has a smaller diameter than the middle portions


46


C described above. Moreover, the second middle portions


46


D preferably has a smoother surface and is preferably machined more accurately than the first middle portions


46


C of the bore


40


. The diameter of the first middle portion


46


C is preferably slightly larger than the diameter of the decompression shaft


34


. As such, a small gap


47


lies between the first middle portions


46


C and the decompression shaft


34


. The two ends of the decompression shaft


34


are supported by bearing collars


52


, which are preferably positioned within the larger diameter portions


46


A,


46


B of the bore


40


near or more preferably at the end of the camshaft


12


. The coupling point


38


of the decompression shaft


34


is supported by the bearing surface


48


. This is arrangement is advantageous because the portions larger diameter portions


46


A,


46


B,


46


C do not need to be machined as smoothly or as accurately as the second middle portion


46


D. Such an arrangement reduces the costs and the difficulties associated with manufacturing the camshaft


12


.




Associated with each decompression pin


44


, the decompression shaft


34


includes a plurality of actuating members


54


. In the illustrated embodiment, each actuating member comprises a ring-like cam groove


56


, which preferably has a generally smooth, curved cross-sectional shape; however, other cam shapes are also possible. In a non-activated position of the decompression shaft (see FIG.


2


A), the grooves


56


are aligned with the pin holes


42


. As such, the decompressions pins


44


, which are biased towards the longitudinal axis


41


, sink into the grooves


56


and do not extend significantly past the outer surface


58


of the camshaft


12


. Thus, in the non-activated position, the decompression pins have no or a very small effect on the position of the exhaust valve


26


. In contrast, when the decompression shaft


34


is in the activated position (see FIG.


2


B), the decompression pins


44


are no longer aligned with the grooves


56


but contact an outer surface


57


of the decompression shaft


34


. As such, the ends of the decompression pins


44


are forced out of the pin holes


42


such that the decompression pins


44


protrude from the outer periphery


58


and push on the bearing surface


30


of the exhaust valve


26


. The pin holes


42


are preferably positioned on the camshaft


12


such that the exhaust valves


26


are lifted during the compression stroke of the associated cylinder. In this manner, the decompression pins


44


“lift” the exhaust valves


26


from a normally closed position and effectively reduce the effective compression ratio of the engine.




Longitudinal movement of the decompression shaft


34


, therefore, switches the decompression system


16


between the activated and non-activated states. To facilitate the movement of the decompression pins


44


in and out of the cam groove


56


, the decompression pins


44


preferably include a corresponding smooth, curved cam surface


59


as best seen in FIG.


2


B. This cam surface


59


interacts with the groove


56


such that the decompression shaft


34


can slide smoothly over the pins


44


.




With continued reference to

FIGS. 2A and 2B

and the illustrated embodiment, the first and second portions


36


A,


36


B of the decompression shaft


34


are coupled together at the coupling point


38


via a tongue and groove arrangement, which is secured by a pin


60


that extends through apertures formed in the tongue and groove arrangement. In modified embodiments, the portions


36


A,


36


B may be coupled in other manners. For example, a key, hook or serration arrangement may be used to couple the two portions


36


A,


36


B together. In another modified embodiment, the first portion


36


A may be threaded into the second portion


36


B. In still another modified embodiment, the two portions


36


A,


36


B can be simply be in contact with each other (i.e., uncoupled). In such an arrangement, a biasing member is needed to bias the decompression shaft into either the activated or non-activated position. The key and serration arrangements are particularly useful in an arrangement wherein the decompression shaft is rotated between the first and second positions as will be described below.




A first end


62


of the decompression shaft


34


preferably extends from the camshaft


12


in both the activated and non-activated positions (see FIGS.


2


A and


2


B). This end


62


of the shaft


34


preferably includes a tapered portion


64


,which transitions the diameter of the shaft


34


to smaller diameter portion


66


. This arrangement is preferred because it facilitates assembly of the decompression system


16


. Specifically, during assembly, the small diameter portion


66


of the decompression shaft


34


is first inserted into the bore


40


of the camshaft


12


. As the decompression shaft


34


is moved through the bore


40


in the direction indicated by the arrow A of

FIG. 2A

, the small diameter portion


66


and the tapered portion


64


gradually push the biasing members and decompression pins


44


inside the pin holes


42


such that the decompression shaft


34


can be smoothly inserted into the bore


40


.




A drive apparatus


68


for actuating the decompression shaft


34


will now be described with reference to

FIGS. 2A-6B

. In the illustrated embodiment, the drive apparatus


68


includes a washer


70


, which may be coupled to the first end


62


of the shaft


34


by a bolt


72


.




The decompression shaft


34


preferably includes a recess or protrusion


74


with one or more flat sides on the second or opposite end


75


of the shaft


34


. The recess or protrusion


74


is used to prevent rotation of the shaft


34


when the washer


70


is being coupled to the shaft


34


by a bolt


72


.




A clamp


76


is coupled to the washer


70


. In the illustrated embodiment, the claim


76


includes a first leg


77


A and a second leg


77


B define a channel in which the washer


70


is positioned. In some arrangements, the legs


77


A,


77


B can be biased towards the washer


70


to positively hold the washer


70


. In other arrangements, the legs


77


A,


77


B are arranged so as to only contact the washer


70


. The clamp


70


pivots about a stay


78


, which has an axis


80


that is generally perpendicular to the longitudinal axis


41


of the camshaft as best seen in

FIGS. 1 and 5

. The clamp


70


is coupled to a bracket


82


, which also pivots about the stay


78


as seen in FIG.


4


. The bracket


82


, in turn, is coupled to a bowden-wire


84


, which may be coupled to an actuator provided near a control panel for the engine. For example, the wire


84


may be coupled to a lever provided on a handlebar. In a modified embodiment, the bowden-wire is arranged so as to be activated when a starter motor is activated such that the decompression system


16


is automatically activated.




As best seen in

FIG. 4

, a torsional spring


86


is preferably provided on the stay


78


. The torsional spring


86


preferably biases the decompression system


16


to a nonactivated position (i.e., the position shown in FIG.


2


A).




With particular reference to

FIGS. 4

,


6


A and


6


B, the operation of the decompression system


16


will be described in more detail. When the bowden-wire


84


is pulled in the direction indicated by arrow B in

FIG. 4

, the bracket


82


and the clamp


76


rotate about the axis


80


as indicated by arrow C. As shown in

FIGS. 6A and 6B

, this rotation pushes the decompression shaft


34


in the direction indicated by arrow D.




In the initial deactivated position (FIG.


6


A), the grooves


56


are aligned with the pin holes


42


. As such, the decompressions pins


44


, which are biased towards the longitudinal axis


41


, sink into the grooves


56


and do not extend significantly past the outer surface


58


of the camshaft


12


. Thus, in the non-activated position, the decompression pins have no or a very small effect on the position of the corresponding exhaust valve


26


. As the decompression shaft


34


is moved in the direction of arrow D, the decompression shaft


34


is moved to the activated position (FIG.


6


B). In the position, the decompression pins


44


are no longer aligned with the grooves


56


. As such, the ends of the decompression pins


44


are forced out of the pin holes


42


such that the decompression pins


44


protrude from the outer periphery


58


and push on the bearing surface


30


of the exhaust valve


26


during the compression stroke. In this manner, the decompression pins


44


“lift” the exhaust valves


26


and effectively reduce the effective compression ratio of the engine. Thus, longitudinal movement of the decompression shaft


34


switches the decompression system


16


between the activated and non-activated states. As the decompression shaft


34


moves longitudinally the grooves


56


and the cam surface


59


of the pin


44


glide over each other such that the movement of the decompression shaft is smooth.




The decompression system


16


described above has several advantages. For example, because the decompression shaft


34


is formed in two portions


36


a,


36


B, the decompression shaft


34


can be manufactured more easily and more reliably as compared to a single decompression shaft. This is particularly advantageous for engines with several cylinders, wherein the camshafts are particularly long. In such engines, the bore


40


of the camshaft


12


maybe difficult to machine accurately.




Another advantage of the preferred embodiment is that the decompression shaft


34


is supported by a bearing surface


48


, which is preferably located at the junction


38


. The remaining portions


46


A,


46


B,


46


C of the bore


40


have diameter larger than the decompression shaft


34


. As such, the remaining portions


46


A,


46


B,


46


C of the bore


40


can be less smooth and machine less accurately than the bearing surface


48


. This also reduces the costs of manufacturing and assembling the decompression system


16


.




In the illustrated embodiment described above, the decompression shaft


34


moves longitudinally along the longitudinal axis


41


of the camshaft


12


. As such, longitudinally movement of the decompression shaft


34


is used to actuate the decompression pins


44


. In a modified embodiment, the decompression system


16


can be arranged such that rotation of the decompression shaft


34


about the longitudinal axis


41


actuates the decompression pins


44


. In such an arrangement, the decompression shaft


34


include cam surfaces that vary the diameter of the decompression shaft as the decompression shaft


34


is rotated. Thus, as the decompression shaft


34


is rotated in a first direction, the decompression pins


44


are pushed out of the pin holes


42


to impart lift to the exhaust valves


26


. The drive apparatus


68


can be modified to impart rotation on the camshaft


12


. The rotation of the cam shaft may be automatic in response to the rotational speed of the engine. See e.g., U.S. Pat. No. 6,073,599, which is hereby expressly incorporated by reference herein. In such an arrangement, the decompression shaft preferably rotates with the camshaft


12


.




In the illustrated embodiment, the camshaft


12


rotates about the decompression shaft


34


, which does not rotate. However, in a modified embodiment, the decompression shaft


34


can rotate with the camshaft


12


. In one application of such an arrangement, the washer


70


can rotate with respect to the clamp


76


, which can remain stationary. It should be noted that in such an arrangement the camshaft


12


and the decompression shaft


34


need not be coaxial.




In the illustrated embodiment, the decompression shaft


34


is positioned within the exhaust camshaft


12


. However, it should be appreciated that the decompression shaft can be positioned within the intake camshaft


14


instead of or in addition to the exhaust camshaft


12


.




Of course, the foregoing description is that of preferred embodiments of the invention and various changes, modifications, combinations and sub-combinations may be made without departing from the spirit and scope of the invention, as defined by the appended claims.



Claims
  • 1. A decompression system for a four-cycle engine comprising a camshaft, decompression shaft, and at least one decompression pin, the camshaft having at least one cam arranged to activate a valve of the engine, an internal bore that extends generally longitudinally with respect to the camshaft and at least one pin hole arranged generally perpendicular to the internal bore, the decompression shaft comprising a first longitudinal portion and a second separate longitudinal portion that are configured to fit within the internal bore of the camshaft, means for detachably coupling the first longitudinal portion of the decompression shaft to the second separate longitudinal portion of the decompression shaft such that longitudinal movement of the first portion in the bore is transferred to the second portion, the decompression shaft moveable between a first position and a second position and further comprising at least one cam surface having a first portion and a second portion, the cam surface arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve.
  • 2. A decompression system as in claim 1, further comprising a biasing member to bias the decompression shaft in either the first or second position.
  • 3. A method of assembling a decompression system for an engine comprising, forming a bore within the camshaft, the bore having a middle portion with a first diameter and a second portion with a second diameter that is larger than the first diameter, forming at least one pin hole in the camshaft, the pin hole extending generally perpendicular to a longitudinal axis of the camshaft, inserting a pin into the pin hole, forming a first portion of a decompression shaft, forming a second separate portion of a decompression shaft, detachably coupling the first portion of the decompression shaft to the second separate portion of the decompression shaft and inserting the first portion and the second separate portion of the decompression shaft into the bore such that longitudinal movement of the first portion in the bore is transferred to the second portion.
  • 4. The method of assembling as in claim 3, comprising positioning the decompression shaft within the camshaft such that a junction between the first and second portions is located near a longitudinal center of the camshaft.
  • 5. A decompression system for a four-cycle engine comprising a camshaft, decompression shaft, and at least one decompression pin, the camshaft having at least one cain arranged to activate a valve of the engine, an internal bore that extends generally longitudinally with respect to the camshaft, and at least one pin hole arranged generally perpendicular to the internal bore, the decompression shaft comprising a first longitudinal portion and a second longitudinal portion that are configured to fit within the internal bore of the camshaft, the decompression shaft moveable between a first position and a second position and further comprising at least one cam surface having a first portion and a second portion, the cam surface arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve, wherein the first portion and the second portion of the decompression shaft are coupled together by a pin.
  • 6. A decompression system for a four-cycle engine comprising a camshaft, decompression shalt and at least one decompression pin, the camshaft having at least one cam arranged to activate a valve of the engine, an internal bore that extends generally longitudinally with respect to the camshaft, and at least one pin hole arranged generally perpendicular to the internal bore, the decompression shaft comprising a first longitudinal portion and a second longitudinal portion that are configured to fit within the internal bore of the camshaft, the decompression shaft moveable between a first position and a second position and further comprising at least one cam surface having a first portion and a second portion, the cam surface arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve, wherein one end of the decompression shaft extends past an end of the camshaft and the one end of the decompression shaft is coupled to drive apparatus for moving the decompression shaft between the first and second positions, the one end of the decompression shaft comprising a distal portion with a first diameter, a tapered portion, and a proximal portion with a second diameter, the first diameter being smaller than the second diameter and the tapered portion extending from the proximal portion to the distal portion.
  • 7. A decompression system for a four-cycle engine comprising a camshaft, decompression shaft, and at least one decompression pin, the camshaft having at least one cam arranged to activate a valve of the engine, an internal bore that extends generally longitudinally with respect to the camshaft, and at least one pin hole arranged generally perpendicular to the internal bore, the decompression shaft comprising a first longitudinal portion and a second separate longitudinal portion that are configured to fit within the internal bore of the camshaft, the first and second longitudinal portions including inter-engaging structures that detachably couple the second longitudinal portion to the first longitudinal portion such that longitudinal movement of the first longitudinal portion in the bore is transferred to the second longitudinal portion, the decompression shaft moveable between a first position and a second position and further comprising at least one cam surface having a first portion and a second portion, the cam surface arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve.
  • 8. A decompression system as in claim 7, wherein the decompression shaft moves longitudinally with respect to a longitudinal rotational axis of the camshaft when moving between the first position and the second position.
  • 9. A decompression system as in claim 7, wherein first and second bearings journal the decompression shaft for rotation with respect to the camshaft.
  • 10. A decompression system as in claim 7, wherein the first portion of the decompression shaft is journaled for longitudinal movement within the camshaft by a first bearing positioned within the bore and the second portion of the decompression shaft is journaled for movement within the camshaft by a second bearing also positioned within the bore.
  • 11. A decompression system as in claim 10, wherein a coupling point between the first and second portions of the decompression shaft is supported by a third bearing.
  • 12. A decompression system as in claim 11, wherein the decompression shaft is supported in the camshaft only by the first, second and third bearings.
  • 13. A decompression system as in claim 11, wherein the third bearing is formed by an inner wall of the camshaft's internal bore.
  • 14. A decompression system as m claim 11, wherein the third bearing also journal the decompression shaft for rotation with respect to the camshaft.
  • 15. A decompression system as in claim 7, wherein the first and second bearings are located near the ends of the camshaft.
  • 16. A decompression system as in claim 7, wherein a coupling point between the first and second portions of the decompression shaft is located near a longitudinal center of the camshaft.
  • 17. A decompression system as in claim 7, wherein one end of the decompression shaft extends past an end of the camshaft.
  • 18. A decompression system as in claim 17, wherein the one end of the decompression shaft is coupled to drive apparatus for moving the decompression shaft between the first and second positions.
  • 19. A decompression system as in claim 17, wherein the one end of the decompression shaft comprises a distal portion with a first diameter, a tapered portion, and a proximal portion with a second diameter, the first diameter being smaller than the second diameter and the tapered portion extending from the proximal portion to the distal portion.
  • 20. A decompression system as in claim 7, wherein the camshaft is an exhaust camshaft of the engine.
  • 21. A decompression system for a four-cycle engine comprising a camshaft, decompression shaft, and at least one decompression pin, the camshaft having at least one cam arranged to activate a valve of the engine, an internal bore that extends generally longitudinally with respect to the camshaft, and at least one pin hole arranged generally perpendicular to the internal bore, the decompression shaft comprising a first longitudinal portion and a second separate longitudinal portion that are configured to fit within the internal bore of the camshaft, the decompression shaft moveable between a first position and a second position and further comprising at least one cam surface having a first portion and a second portion, the cam surface arranged such that in the first position of the decompression shaft the first portion of the cam surface allows the decompression pin to withdraw and in a second position of the decompression shaft the second portion of the cam surface causes the decompression pin to protrude and lift the valve, and a coupling member for detachably coupling the first longitudinal portion of the decompression shaft to the second separate longitudinal portion of the decompression shaft.
  • 22. A decompression system as in claim 21, wherein the decompression shaft moves longitudinally with respect to a longitudinal rotational axis of the camshaft when moving between the first position and the second position.
  • 23. A decompression system as in claim 21, wherein first and second bearings journal the decompression shaft for rotation wit respect to the camshaft.
  • 24. A decompression system as in claim 23, wherein the first portion of the decompression shaft is journaled for longitudinal movement within the camshaft by a first bearing positioned within the bore and the second portion of the decompression shaft is journaled for movement within the camshaft by a second bearing also positioned within the bore.
  • 25. A decompression system as in claim 24, wherein a coupling point between the first and second portions of the decompression shaft is supported by a third bearing.
  • 26. A decompression system as in claim 25, wherein the decompression shaft is supported in the camshaft only by the first, second and third bearings.
  • 27. A decompression system as in claim 25, wherein the third bearing is formed by an inner wall of the camshaft's internal bore.
  • 28. A decompression system as in claim 25, wherein the third bearing also journal the decompression shaft for rotation with respect to the camshaft.
  • 29. A decompression system as in claim 25, wherein the first and second bearings are located near the ends of the camshaft.
  • 30. A decompression system as in claim 21, wherein a coupling point between the first and second portions of the decompression shaft is located near a longitudinal center of the camshaft.
  • 31. A decompression system as in claim 21, wherein one end of the decompression shaft extends past an end of the camshaft.
  • 32. A decompression system as in claim 21, wherein the one end of the decompression shaft is coupled to drive apparatus for moving the decompression shaft between the first and second positions.
  • 33. A decompression system as in claim 31, wherein the one end of the decompression shaft comprises a distal portion with a first diameter, a tapered portion, and a proximal portion with a second diameter, the first diameter being smaller than the second diameter and the tapered portion extending from the proximal portion to the distal portion.
  • 34. A decompression system as in claim 21, wherein the camshaft is an exhaust camshaft of the engine.
Priority Claims (1)
Number Date Country Kind
2001-107433 Apr 2001 JP
RELATED APPLICATIONS

This application is based upon Japanese Patent Application No. 2001-107433, filed on Apr. 5, 2001, which is hereby expressly incorporated by reference in its entirety.

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03182613 Aug 1991 JP
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