Handheld type four-cycle engine

Abstract: In a handheld type OHV engine, an oil tank (13) is provided so as to be connected to one side wall running the length of a crankcase (6) and a cylinder block (7), the oil tank (13) houses oil mist generation means (36,37,38,39,40) to and a rotational movement section of a valve operation mechanism, and the oil mist generated in the oil tank is supplied from a crank chamber to a valve operation chamber of a cylinder head housing a reciprocating movement section of the valve operation mechanism, and is returned to the oil tank by utilising the pressure pulsations of the crank chamber and a one-way valve (51). It is thus possible to lubricate the inside of the crank chamber and the valve operation mechanism reliably regardless of the operational position of the handheld type OHV engine while reducing the overall height of the engine.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a handheld type four-cycle engine which is mainly used as a power source for portable working apparatus such as a trimmer. More particularly, it relates to improvement of the so-called OHV engine that includes an engine main body, the engine main body including a crankcase having a crank chamber, a cylinder block having a cylinder bore, and a cylinder head having an intake port and an exhaust port; a crankshaft supported in the crankcase and housed inside the crank chamber; a piston fitted in the cylinder bore and connected to the crankshaft; an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and exhaust valve being mounted in the cylinder head; and a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and exhaust valve. DESCRIPTION OF THE RELATED ART As such an OHV engine which is already known, for example, Japanese Patent Application Laid-open No. 10-288019 discloses one in which an oil reservoir is provided in the lower part of a crankcase, an oil mist is generated by scattering the oil stored in the oil reservoir by the rotation of a crankshaft, and the inside of the engine is lubricated with the oil mist. Generally, OHV engines having intake and exhaust valves in their cylinder head tend to be large in overall height due to the presence of the intake and exhaust valves and a valve operation mechanism for opening and closing them. However, an oil reservoir is formed in the lower part of the crankcase as in the above-mentioned conventional engine, the overall height is further increased and it becomes difficult to make the engine more compact. SUMMARY OF THE INVENTION The present invention has been carried out in view of the above-mentioned circumstances. It is an object of the present invention to lubricate the inside of the crank chamber and the valve operation mechanism reliably regardless of the operational position of the engine, while reducing the overall height of the engine so making it more compact. In accordance with a first aspect of the present invention in order to achieve the above-mentioned objective, there is proposed a handheld type four-cycle engine including an engine main body, the engine main body including a crankcase having a crank chamber, a cylinder block having a cylinder bore, and a cylinder head having an intake port and an exhaust port; a crankshaft supported in the crankcase and housed inside the crank chamber; a piston fitted inside the cylinder bore and connected to the crankshaft; an intake valve and an exhaust valve for opening and closing the intake port and exhaust port, the intake valve and the exhaust valve being mounted in the cylinder head; and a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and the exhaust valve, wherein an oil tank for storing oil is provided so as to be connected to one side wall running the length of the crankcase and the cylinder block; the oil tank houses oil mist generation means for generating an oil mist from the stored oil, and a rotational movement section of the valve operation mechanism; the oil tank and the crank chamber are communicated with each other above the stored oil in the oil tank; the crank chamber and a valve operation chamber formed in the cylinder head so as to house a reciprocating movement section of the valve operation mechanism are communicated with each other via an oil feed passage; the valve operation chamber and the oil tank are communicated with each other above the stored oil in the oil tank via an oil return passage; and transfer means for sending only the positive pressure component of pressure pulsations generated in the crank chamber towards the valve operation chamber is provided in the oil feed passage. The above-mentioned transfer means corresponds to the one-way valve 51 in the embodiments of the present invention below. In accordance with the above-mentioned first characteristic, since the oil tank is provided so as to be connected to one side wall running the length of the crankcase and the cylinder block, it is unnecessary to provide an oil reservoir in the lower part of the crankcase, and the overall height of the engine can thus be reduced and the engine can be made more compact. Furthermore, since the oil tank is filled with the oil mist generated by the oil mist generation means, the rotational section of the valve operation mechanism provided inside the oil tank can be lubricated with the oil mist particularly well. Moreover, since the oil mist inside the oil tank is supplied to the crank chamber and the valve operation chamber, and returned to the oil tank by utilising the pressure pulsations of the crank chamber, the inside of the crank chamber and the reciprocating movement section of the valve operation mechanism can be lubricated regardless of the operational position of the engine, and it is unnecessary to employ a special oil pump for circulating the oil mist so simplifying the structure. In accordance with a second aspect of the present invention, in addition to the above-mentioned characteristic, there is proposed a handheld type four-cycle engine wherein an oil mist is generated by the motion of the rotational movement section of the valve operation mechanism scattering the stored oil inside the oil tank. In accordance with the above-mentioned second characteristic, since the rotational section of the valve operation chamber functions as part of the oil mist generation means, the oil mist generation means can be obtained in a simple manner. The above-mentioned object, other objects, characteristics and advantages of the present invention will become apparent from an explanation of preferable embodiments which will be described in detail below by reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1 to 4 illustrate a first embodiment of the present invention. Fig. 1 is an perspective view showing one embodiment of the handheld type four-cycle engine of the present invention in practical use. Fig. 2 is a vertically sectioned front view of the above-mentioned four-cycle engine. Fig. 3 is a cross-sectional view at line 3-3 in Fig. 2. Fig. 4 is a cross-sectional view at line 4-4 in Fig. 2. Fig. 5 is a cross-sectional view corresponding to Fig. 4 and illustrating a second embodiment of the present invention. Fig. 6 is a cross-sectional view corresponding to Fig. 4 and illustrating a third embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS The first embodiment of the present invention shown in Figs. 1 to 4 is explained first. As shown in Fig. 1, a handheld type four-cycle engine E to which the present invention is applied is fitted as the source of power to the drive section of, for example, a powered trimmer T. Since the powered trimmer T is used in a manner in which a cutter C is positioned in various directions according to the operational conditions, the engine E is also tilted to a large extent or turned upside-down as a result and the operational position is unstable. As shown in Figs. 2 and 3, the engine main body 1 of the above-mentioned handheld type four-cycle engine E includes a crankcase 6 having a crank chamber 6a, a cylinder block 7 having one cylinder bore 7a, and a cylinder head 8 having a combustion chamber 8a, a large number of cooling fins 11 being formed on the outer peripheries of the cylinder block 7 and the cylinder head 8. A crankshaft 12 housed in the crank chamber 6a is rotatably supported in left and right side walls of the crankcase 6 via ball bearings 14 and 14' and is also connected to a piston 15 fitted in the cylinder bore 7a via a connecting rod 16. An oil seal 17 is fitted in the left-hand side wall of the crankcase 6 so as to adjoin the outside of the bearing 14, a flywheel 26 having a large number of cooling vanes 26a is fixed to the left-hand end of the crankshaft 12 running through the oil seal 17 and projecting out of the crankcase 6, the flywheel 26 functioning also as a cooling fan, and a recoil type starter 64 is positioned outside the flywheel 26. An oil tank 13 is provided so as to be connected to the right-hand side wall running the length of the crankcase 6 and the cylinder block 7. A fuel tank 5 is provided on one side of the oil tank 13 and beneath a carburettor 2 and an air cleaner 4 which will be described below. The oil tank 13 includes a tank inner half 13a and a tank outer half 13b, the tank inner half 13a being integrally provided over the crankcase 6 and the cylinder block 7, and the tank outer half 13b being bolt-joined to the tank inner half 13a. The right-hand end of the crankshaft 12 runs through and projects out of the oil tank 13. An oil seal 17' in close contact with the outer circumference of the crankshaft 12 is fitted in the tank outer half 13b. A drive plate 27 is fixed to the right-hand end of the crankshaft 12 projecting out of the oil tank 13, and a plurality of centrifugal shoes 28 (one thereof is shown in the figure) are pivotally supported on the drive plate 27 in a rockable manner. These centrifugal shoes 28, together with a clutch drum 30 connected to a drive shaft 29 for driving the aforementioned cutter C, form a centrifugal clutch 31 and when the rotational rate of the crankshaft 12 exceeds a predetermined value, the centrifugal shoes 28 are pressed onto the inner periphery of the clutch drum 30 due to the centrifugal force of the shoes so transmitting the output torque of the crankshaft 12 to the drive shaft 29. An engine cover 65 is fixed to the engine main body 1 so as to cover it, a recoil type starter 64 is supported in the cover 65, and an air inlet 66 is provided in the engine cover 65 around the recoil type starter 64 so as to face the cooling vanes 26a of the flywheel 26. An intake port 9i and an exhaust port 9e opening into the combustion chamber 8a are formed in the cylinder head 8, and the cylinder head 8 is also provided with an intake valve 18i and an exhaust valve 18e and an ignition plug 63, the intake valve 18i and the exhaust valve 18e opening and closing the intake port 9i and the exhaust port 9e, and the electrodes of the ignition plug 63 extending into the combustion chamber 8a. A rocker chamber 19a whose upper face is blocked by a head cover 10 is provided in the cylinder head 8, a pushrod chamber 19b extending from one side of the rocker chamber 19a down to the top of the oil tank 13 is formed in one side wall of the cylinder block 7, and the rocker chamber 19a and the pushrod chamber 19b together form a valve operation chamber 19. A valve operation mechanism 25 for closing and opening the intake and exhaust valves 18i and 18e is provided running through the valve operation chamber 19 and the oil tank 13. That is to say, the valve operation mechanism 25 includes a rotational movement section 25a housed in the oil tank 13 and a reciprocating movement section 25b housed in the valve operation chamber 19. The rotational movement section 25a includes a drive gear 32 fixed to the crankshaft 12, a cam gear 36 rotatably supported on a support shaft 33 and meshed with the drive gear 32, the two ends of the support shaft 33 being supported in the oil tank 13, and an intake cam 21 i and an exhaust cam 21 e formed integrally with the cam gear 36, and the cam gear 36 is driven by the drive gear 32 at a reduction rate of 1/2. The drive gear 32 and the cam gear 36 are positioned above the crankshaft 12 and close to the outside wall of the oil tank 13. The reciprocating movement section 25b includes valve springs 20i and 20e forcing the intake and exhaust valves 18i and 18e respectively in the closed direction, rocker arms 22i and 22e supported in a rockable manner in the cylinder head 8, one end of each of the rocker arms 22i and 22e being in contact with the corresponding upper ends of the intake and exhaust valves 18i and 18e, and pushrods 23i and 23e (see Fig. 4), the upper end of each of the pushrods 23i and 23e being in contact with the corresponding other ends of the rocker arms 22i and 22e. The rocker arms 22i and 22e are housed in the rocker chamber 19a, and the pushrods 23i and 23e are housed in the pushrod chamber 19b. Tappets 24i and 24e receiving the lower end of each of the pushrods 23i and 23e and engaging with the intake and exhaust cams 21i and 21e respectively are fitted in a sliceable manner in guide holes 43 and 43 in a partition wall 42 between the pushrod chamber 19b and the oil tank 13. The engine E is thus constructed as an OHV type. When the intake and exhaust cams 21i and 21 e are rotated by the crankshaft 12 via the drive gear 32 and the cam gear 36, these cams 21i and 21e work together with the valve springs 20i and 20e, and allow the corresponding pushrods 23i and 23e to ascend and descend alternately so as to rock the rocker arms 22i and 22e, and the intake and exhaust valves 18i and 18e are thus opened and closed alternately with appropriate timing. As shown in Fig. 3, the intake port 9i is connected to a carburettor 2 and an air cleaner 4 in that order, and the exhaust port 9e is connected to an exhaust muffler 3. The carburettor 2 and the exhaust muffler 3 are placed along a direction perpendicular to the axes of both the crankshaft 12 and the cylinder bore 7a. The lubrication system of the engine E is explained below by reference to Figs. 2 and 4. An end of each of two support shafts 34 and 35 arranged around and beneath the crankshaft 12 is supported in the oil tank 13, and toothed oil slingers 37 and 38 meshed with the above-mentioned drive gear 32 are rotatably supported on the support shafts 34 and 35. These toothed oil slingers 37 and 38 are positioned close to the outside wall of the oil tank 13 in the same way as the cam gear 36, and vane type oil slingers 39 and 40 positioned close to the inside wall of the oil tank 13 are joined integrally to the corresponding toothed oil slingers 37 and 38 via bosses. As shown in Fig. 4, the above-mentioned cam gear 36 and the two toothed oil slingers 37 and 38 are positioned with equal intervals therebetween around the crankshaft 12. The peripheral wall of the oil tank 13 is formed in a circular shape so as to surround these gears 36 to 38, a predetermined amount of lubricating oil O is stored inside the oil tank 13, at least one of the cam gear 36, the toothed oil slingers 37 and 38 and the vane type oil slingers 39 and 40 around the drive gear 32 is partially immersed in the stored oil O regardless of the operational position of the engine E, and its rotation scatters the stored oil O so generating an oil mist. The cam gear 36 therefore also functions as part of the oil slingers around the drive gear 32. The route taken by the oil mist generated in the oil tank 13 includes an oil inlet 45 provided in the crankshaft 12 and providing communication between the oil tank 13 and the crank chamber 6a, a valve hole 47 provided in the base of the crank case 6, a valve chamber 48 formed in the lower part of the crankcase 6 and communicated with the crank chamber 6a via the above-mentioned valve hole 47, an oil feed passage 49 rising from one side of the valve chamber 48 and extending to the rocker chamber 19a through a side wall of the engine main body 1, the rocker chamber 19a, the pushrod chamber 19b, and an oil return passage 50 extending from the pushrod chamber 19b to the oil tank 13 through the outside wall of the oil tank 13. Open ends 45a and 50a of the above-mentioned oil inlet 45 and the oil return passage 50 inside the oil tank 13 are positioned so as to be always above the liquid level of the stored oil O regardless of the operational position of the engine E. The above-mentioned valve chamber 48 includes a one-way valve 51 in the form of a reed valve for blocking and unblocking the valve hole 47, and the one-way valve 51 opens so as to unblock the valve hole 47 when the pressure of the crank chamber 6a becomes positive and closes so as to block the valve hole 47 when the pressure becomes negative accompanying the descent and ascent respectively of the piston 15. In Figs. 3 and 4, a flat-shaped first breather chamber 53a forming the middle part of the oil return passage 50 is formed in the partition wall 42 between the valve operation chamber 19 and the oil tank 13, and the first breather chamber 53a is connected to a second breather chamber 53b via a link passage 54, the second breather chamber 53b being formed in the above-mentioned head cover 10. The second breather chamber 53b is communicated with the above-mentioned air cleaner 4 on one side via a first orifice 55a and a breather pipe 56, and with the rocker chamber 19a on the other side via a plurality of second orifices 55b which open at different positions and are in different directions from each other. The action of this embodiment is explained below. When the drive gear 32 rotates together with the crankshaft 12 during operation of the engine E, the valve operation mechanism 25 is operated as mentioned above, and at the same time, the cam gear 36, the toothed oil slingers 37 and 38, and the vane type oil slingers 39 and 40 all supported by the three support shafts 33, 34 and 35 rotate simultaneously. Since at least one of the cam gear 36, the toothed oil slingers 37 and 38, and the vane type oil slingers 39 and 40 scatters the stored oil O so generating an oil mist regardless of the operational position of the engine E, the oil tank 13 can always be filled with the oil mist. Since the rotational movement section 25a of the valve operation mechanism 25 is provided in such an oil tank 13, the rotational movement section 25a can be lubricated with the above-mentioned oil mist particularly well. A negative pressure and a positive pressure are generated alternately in the crank chamber 6a accompanying the ascent and descent of the piston 15 so causing pressure pulsations; when a negative pressure is generated, the one-way valve 51 closes so as to block the valve hole 47, and the oil mist inside the oil tank 13 is drawn up into the crank chamber 6a through the oil inlet 45 of the crankshaft 12 thus lubricating the crankshaft 12 and the piston 15. At this stage, the internal pressure of the oil tank 13 is reduced due to the oil mist drawn up into the crank chamber 6a. When a positive pressure is generated, since the one-way valve 51 opens so as to unblock the valve hole 47, the oil mist inside the crank chamber 6a is discharged together with the blowby gas generated in the crank chamber 6a into the rocker chamber 19a through the valve hole 47, the valve chamber 48 and the oil feed passage 49, so that the oil mist is spread over the entire valve operation chamber 19, and the reciprocating movement section 25b of the valve operation mechanism 25 can thus be lubricated. The oil mist is then liquefied. The oil liquefied inside the valve operation chamber 19 is transferred to the first breather chamber 53a from the upstream section of the oil return passage 50 together with the blowby gas, they are separated into gas and liquid in the first breather chamber 53a, the oil portion is returned into the oil tank 13 which is at a lower pressure via the downstream section of the oil return passage 50, and the blowby gas ascends inside the link passage 54 to enter the second breather chamber 53b, and is discharged into the air cleaner 4 via the second orifice 55b and the breather pipe 56. In the case where the blowby gas entering the second breather chamber 53b contains oil, the oil is separated from the blowby gas in the second breather chamber 53b, and flows down through the link passage 54 or enters the valve operation chamber 19 via the second orifice 55b. Since the second breather chamber 53b is connected to the breather pipe 56 via the first orifice 55a, the first orifice 55a can minimise as much as possible the leakage of negative pressure of the oil tank 13 from the second breather chamber 53b towards the breather pipe 56, and thus the oil tank 13 can always maintain its internal negative pressure rendered by the pressure pulsations of the crank chamber 6a during operation of the engine E. The oil mist can thus be circulated from the oil tank 13 to the crank chamber 6a, the valve operation chamber 19, and back to the oil tank 13 by utilising the pressure pulsations of the crank chamber 6a, the inside of the engine E can be lubricated regardless of the operational position of the engine E, and it is unnecessary to employ a special oil pump. In particular, since the rotational movement section 25a requiring a high level lubrication of the valve operation mechanism 25 is lubricated with a large amount of oil mist generated in the oil tank 13, the rotational movement section 25a can be lubricated well as required. Since the oil tank 13 is provided so as to be connected to one side wall running the length of the crankcase 6 and the cylinder block 7, it is unnecessary to provide an oil reservoir in the lower part of the crankcase 6, and the overall height of the engine E can be lessened and the size thereof can be reduced. The second and third embodiments of the present invention are explained below by reference to Figs. 5 and 6. The second and third embodiments are different from the first embodiment in terms of the arrangement of the toothed oil slingers 37 and 38 around the drive gear 32, the shape of the peripheral wall of the oil tank 13, and the shape and arrangement of the fuel tank 5. That is to say, in the second embodiment shown in Fig. 5, the two toothed oil slingers 37 and 38 are placed immediately beside and immediately below the drive gear 32 respectively, and the peripheral wall of the oil tank 13 is generally made in the form of a D-shape around the oil slingers 37 and 38 and the cam gear 36, immediately above the drive gear 33. Since there is a comparatively large space outside the vertical wall 13w of the oil tank 13 so formed, a fuel tank 5 having a large capacity can be placed in this space. In the third embodiment shown in Fig. 6, the two toothed oil slingers 37 and 38 are placed on either side of the drive gear 32 so as to be close to the cam gear 36 placed above the two oil slingers 37 and 38, and the peripheral wall of the oil tank 13 is made in the form of a rounded triangle around the cam gear 36 and the oil slingers 37 and 38. The oil tank 13 so formed has a shallow base, and since there is a flat space below the oil tank 13, an L-shaped fuel tank 5 having a large capacity can be disposed from one side to the base of the oil tank 13. The components in Figs. 5 and 6 corresponding to those in the first embodiment are denoted by the same reference numerals and are not explained. As is clear from the above-mentioned first to third embodiments, by selecting the positions of the support shafts 33, 34 and 35 placed around the drive gear 32, that is to say, the positions of the cam gear 36 and the toothed oil slingers 37 and 38, the shape of the peripheral wall of the oil tank 13 surrounding them can be changed freely, and the degree of freedom in the layout of equipment adjoining the oil tank 13 increase. Moreover, since the cam gear 36 and the toothed oil slingers 37 and 38 are simultaneously driven by the drive gear 32 in such a state that they are close to the peripheral wall of the oil tank 13, the stored oil O can be scattered by at least one of the cam gear 36 and the toothed oil slingers 37 and 38 regardless of the operational position of the engine E so always generating an oil mist reliably. Since the cam gear 36 functions as part of the oil slingers provided around the driven gear 32, the number of special oil slingers can be reduced and the structure can thus be simplified. The present invention is not limited to the above-mentioned embodiments and can be modified in a variety of ways without departing from the spirit and scope of the invention. For example, a rotary valve operable in association with the crankshaft 12 and operating so as to unblock the oil feed passage 49 when the piston 15 descends and to block the oil feed passage 49 when the piston 15 ascends can be provided instead of the one-way valve 51. In a handheld type OHV engine, an oil tank is provided so as to be connected to one side wall running the length of a crankcase and a cylinder block, the oil tank houses oil mist generation means to and a rotational movement section of a valve operation mechanism, and the oil mist generated in the oil tank is supplied from a crank chamber to a valve operation chamber of a cylinder head housing a reciprocating movement section of the valve operation mechanism, and is returned to the oil tank by utilising the pressure pulsations of the crank chamber and a one-way valve. It is thus possible to lubricate the inside of the crank chamber and the valve operation mechanism reliably regardless of the operational position of the handheld type OHV engine while reducing the overall height of the engine.

Claims: A handheld type four-cycle engine including an engine main body, the engine main body (1) including a crankcase (6) having a crank chamber, a cylinder block having a cylinder bore and a cylinder head having an intake port and an exhaust port; a crankshaft (12) supported in the crankcase and housed inside the crank chamber; a piston fitted inside the cylinder bore and connected to the crankshaft; an intake valve (18i) and an exhaust valve (18e) for opening and closing the intake port and exhaust port, the intake valve and the exhaust valve being mounted in the cylinder head; and a valve operation mechanism operable in association with the rotation of the crankshaft so as to open and close the intake valve and the exhaust valve, wherein an oil tank (13) for storing oil is provided so as to be connected to one side wall running the length of the crankcase and the cylinder block; the oil tank (13) houses oil mist generation means for generating an oil mist from the stored oil, and a rotational movement section of the valve operation mechanism; the oil tank (13) and the crank chamber (6a) are communicated with each other above the stored oil in the oil tank; the crank chamber (6a) and a valve operation chamber formed in the cylinder head so as to house a reciprocating movement section of the valve operation mechanism are communicated with each other via an oil feed passage; the valve operation chamber and the oil tank are communicated with each other above the stored oil in the oil tank via an oil return passage; and transfer means (51) for sending only the positive pressure component of pressure pulsations generated in the crank chamber towards the valve operation chamber is provided in the oil feed passage. A handheld type four-cycle engine according to Claim 1 wherein the stored oil inside the oil tank is scattered by the motion of the rotational movement section of the valve operation mechanism, thereby generating an oil mist.

Inventors: ITO KEITA, NISHIDA TAKAO, WATANABE SEI, ITO, KEITA, NISHIDA, TAKAO, WATANABE, SEI
Applicants: HONDA MOTOR CO LTD, HONDA GIKEN KOGYO KABUSHIKI KAISHA
Application year: 2001
Main classification: F01M1
IPC codes: F01M9, F01L1, F01M11, F02B63, F02B75, F01M1