AU728073B2 - Operator carried power tool having a four-cycle engine - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 DIVISIONAL APPLICATION NAME OF APPLICANT(S): Ryobi Outdoor Products Inc.

ADDRESS FOR SERVICE: DAVIES COLLISON CAVE Patent Attorneys 1 Little Collins Street Melbourne, 3000.

INVENTION TITLE: "Operator carried power tool having a four-cycle engine" The following statement is a full description of this invention, including the best method of performing it known to us: QAOPER\RSH\692382-I .238 27/8/98 P:\OPERSSHMS19687-98 spe 125.doc-9 May 2000 -1A- OPERATOR CARRIED POWER TOOL HAVING A FOUR-CYCLE ENGINE This invention relates to operator carried power tools and more particularly, to operator carried power tools driven by a small internal combustion engine. The invention also relates to an engine for such a tool.

Portable operator carried power tools such as line trimmers, blower/vacuums, or chain saws are currently powered by two-cycle internal combustion engines or electric 0 0*.

:6 10 motors. With the growing concern regarding air pollution, there is increasing pressure to 00:0., .06:0. reduce the emissions of portable power equipment. Electric motors unfortunately have *000:limited applications due to power availability for corded products and battery life for cordless devices. In instances where weight is not an overriding factor such as lawn mowers, emissions can be dramatically reduced by utilizing heavier four-cycle engines.

15 When it comes to operator carried power tools such as line trimmers, chain saws and blower/vacuums, four-cycle engines pose a very difficult problem. Four-cycle engines tend to be too heavy for a given horsepower output and lubrication becomes a very serious problem since operator carried power tools must be able to run in a very wide range of orientations.

The California Resource Board (CARB) in 1990 began to discuss with the industry, particularly the Portable Power Equipment Manufacturer's Association (PPEMA), the need to reduce emissions. In responding to the CARB initiative, the PPEMA conducted a study to evaluate the magnitude of emissions generated by two-cycle engines in an effort to determine whether they were capable of meeting the proposed preliminary CARB standards tentatively scheduled to go into effect in 1994. The PPEMA study concluded that at the present time, there was no alternative power source to replace the versatile lightweight two-stroke engine currently used in hand held products. Four-cycle engines could only be used in limited situations, such as in portable wheeled products like lawn mowers or generators, where the weight of the engine did not have to be borne by the operator.

P:OPER\RSHl\SI19687-98 spe 125.do-9 May. 2000 -2- According to the present invention, there is provided a four-cycle internal combustion engine comprising: an engine block defining a cylindrical bore, a cylinder head, a piston mounted for reciprocation in said cylindrical bore, said cylinder head defining a combustion chamber; an air-fuel mixture intake port and an exhaust gas port defined in said cylinder head assembly; a valve cover on said cylinder head defining a valve chamber; intake and exhaust valves mounted in said intake and exhaust ports, respectively, for reciprocation between port-open and port-closed positions; 10 a valve-actuating valve train, said valve train including at least one rocker arm and at least one valve train push rod assembly extending at one end thereof within said valve chamber and engaging said rocker arm; a crankshaft rotatably mounted in said engine block including a crank position and a counterweight; a connecting rod assembly having at one end thereof articulated connections to said piston and at the opposite end thereof to said crank portion thereby forming a piston- S connecting rod crankshaft assembly; 0 0 0 oooo P:AOPERUSH\819687-98 sp 125.doc-9 May, 2000 -3a cam rotatably driven by said crankshaft and driven at one-half crankshaft speed, the opposite ends of said push rod assembly being drivably connected to said cam whereby said push rod assembly is actuated with a reciprocating motion upon rotation of said cam; said cylindrical bore, said crankshaft and said cam being located in a common plane; an oil reservoir; an oil mist generator element connected drivably to said crankshaft to engage the lubrication oil in order to create an oil mist in said reservoir which lubricates moving parts within the engine block, said reservoir being in fluid communication with said cylindrical bore whereby pressure within the oil reservoir fluctuates as the piston reciprocates; :flow i passageways extending between said reservoir and said valve chamber, to allow the flow of said oil mist through said passages to lubricate the valve train; and .6*a flow control means providing an oil mist flow path from said reservoir to said valve chamber through said engine block and from said valve chamber to said reservoir and controlling the flow of said oil mist through said passageways to and from said valve chamber whereby oil mist is circulated through said engine, the flow control means being oo, connected to act in synchronisation with increases and decreases in gas pressure in said engine block below said piston as said piston reciprocates in said cylindrical bore.

Further according to the present invention, there is provided a method for lubricating a four-cycle internal combustion engine the engine having an engine block, a reciprocating piston in a cylindrical bore in the engine block, a crankshaft, a cam, a cam gear, a valve actuating valve train, a pair of rocker arms, an oil reservoir and a cylindrical head having a valve cover defining a valve chamber and intake and exhaust valves, the method comprising the steps of: creating within said oil reservoir an oil mist; providing said oil mist to lubricate said piston, said crankshaft, said cam, said cam gear, said pair of rocker arms; the oil mist being further provided to said valve train, said intake and exhaust valves by conducting the oil mist through a passage from said reservoir to the valve POEI\RWSHIS19687-98 sp 12S.dw.9 May. 2xM -4chamber and conducting the oil mist in a return flow passage through said engine block from said valve chamber to said reservoir; and controlling the flow of oil mist from said reservoir to said valve chamber in synchronism with increases and decreases in gas pressure in said engine block below said piston as said piston reciprocates in said cylindrical bore whereby oil mist is distributed to said valve chamber throughout a range of angular orientations of the engine relative to vertical disposition of said cylindrical bore.

Preferred embodiments of the invention seek to enable the following objectives to 10 be achieved: to provide a hand held powered tool which is powered by an internal combustion engine having low emissions and is sufficiently light to be carried by an operator; to provide a portable hand held powered tool powered by a small internal combustion engine having an internal lubrication

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*o• •ooo P:\OPER\RSH\EVERTS.DIV 14/5/96 system enabling the engine to be run at a wide variety of orientations typically encountered during normal operation; to provide a portable power tool to be carried by an operator which is driven by a small lightweight four-cycle engine having an aluminum engine block, an overhead valve train and a splasher lubrication system for generating an oil mist to lubricate the crank case throughout the normal range of operating positions; to provide an oil mist pumping system to pump an oil mist generated in the crank case into the overhead valve chamber.

0. A portable hand held power tool of a preferred embodiment of the present invention intended to be carried by an operator is provided utilising a small four-cycle internal combustion 15 engine as a power source. The four-cycle engine is mounted on a frame to be carried by an operator during normal use. The tool has an implement cooperating with the frame having a rotary driven input member coupled to the crankshaft of the four-cycle engine. The four-cycle engine is provided with a lightweight aluminum engine block having at least one cylindrical bore oriented in a normally upright orientation having an enclosed oil reservoir located therebelow. A crankshaft is pivotably mounted within the engine block. The enclosed oil reservoir when properly filled, enables the engine to rotate at least degrees about the crankshaft axis in either direction without oil within the reservoir rising above the level of the crankshaft counter weight. A splasher is provided to intermittently engage the oil within the oil reservoir to ate a mist to lubricate the engine crank case.

P:WOPER(SH\819687-9pw 12.dow-9 M 0 2000 -6- Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view illustrating a line trimmer incorporating an engine in accordance with a preferred embodiment of the present invention; Figure 2 is a cross-sectional side elevational view of the engine; Figure 3 is an enlarged cross-sectional view of the engine of Figure 2 illustrating the lubrication system; Figure 4 is a partial cross-sectional end view of the engine shown in Figures 2 and 1 3 further illustrating the lubrication system; Figure 5 is a timing diagonal of the lubrication system of the engine; :Figure 6 is a torque versus RPM curve; and Figures 7 and 8 contrast the pull force of a four and a two-cycle engine.

Figure 1 illustrates a line trimmer 20. Line trimmer 20 is used for illustration 15 purposes and it should be appreciated that other hand held power tools tended to be carried by operators such as chain saws or a blower vacuum can be made in a similar fashion.

Line trimmer 20 has a frame 22 which is provided by an elongated aluminum tube. Frame 22 has a pair of handles 24 and 26 to be grasped by the operator during normal use. Strap 28 is placed over the shoulder of the user in a conventional manner in order to more 20 conveniently carry the weight of the line trimmer during use. Attached to one end of the frame generally behind the operator is a four-cycle engine 30. The engine drives a conventional flexible shaft which extends through the center of the tubular frame to drive an implement 32 having a rotary cutting head or the like affixed to the opposite end of the frame. It should be appreciated that in the case of a chain saw or a blower/vacuum, the implement would be a cutting chain or a rotary impeller, respectively.

The engine 150 operates on a conventional four-cycle mode. A spark plug is installed in a spark plug hole formed in the cylinder head so as to project into the enclosed combustion chamber. The intake charge provided by carburetor will preferably have an air fuel ratio which is slightly lean stoichiometric, having an air fuel ratio expressed in .1 terms of stoichiometric ratio which is not less than 1.0. It is important to prevent the P:NOPER\RSH\g19697-98 pg 125Ado.9 ly, 2000 -7engine from being operated rich as to avoid a formation of excessive amounts of hydrocarbon (HC) and carbon monoxide (CO) emissions. Most preferably, the engine will operate during normal load conditions slightly lean of stoichiometric in order to minimize the formation of HC, CO and oxides of nitrogen (NOx). Running slightly lean of stoichiometric air fuel ratio will enable excess oxygen to be present in the exhaust gas thereby fostering post-combustion reduction of hydrocarbons within the muffler and exhaust port.

For use in a line trimmer of the type illustrated in Figure 1, adequate power output S 10 of a small lightweight four-cycle engine is achievable utilizing an engine with a displacement less than 80 cc. Preferably, engines for use in the present invention will have a displacement falling within the range of 20 and 60 cc. Engines of displacement larger than 80 cc. will result in excessive weight to be carried by an operator. Engines of smaller displacement will have inadequate power if operated in such a manner to maintain low 15 emission levels.

~The engine 150 has an engine block with a single cam and dual follower design generally similar to that of Figures 2 and 3 of our earlier application 52279/96 to which reference should be made. Cylinder head 152 is provided with a valve cover 154 to define S 20 enclosed valve chamber 156 therebetween. Valve chamber 156 is coupled to oil reservoir 158 within the engine block. In order to induce the mist ladened air within the oil reservoir 158 to circulate through valve chamber 156, flow control means is provided for alternatively selectively coupling the valve chamber to the oil reservoir via one of a pair of independent fluid passageways.

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As illustrated in Figures 3 and 4, intake push rod tube 160 provides a first passageway connecting the oil reservoir to the valve chamber, while exhaust push rod tube 162 provides a second independent passageway connecting the valve chamber 156 to the oil reservoir 158. As illustrated in Figure 3, port B connects push rod tube 162 to the cylindrical bore 166. Port B intersects the cylindrical bore at a location which is swept by the skirt of piston 168 so that the port is alternatively opened and closed in response to piston S. movement. Camshaft 170 is pivotally mounted on a hollow Stubular shaft 172. Camshaft 170 and support shaft 172 are each provided with a pair of ports A which are selectively coupled and uncoupled once every engine S..revolution, twice every camshaft revolution. When the ports are aligned, the oil reservoir is fluidly coupled to the valve chamber via the intake push rod tube 160. When the ports are misaligned, the flow path is blocked.

Figure 5 schematically illustrates the open and close relationship of the A and B ports relative to crankcase pressure. When the piston is down and the crankcase is pressurized, the A port is open allowing -9mist ladened air to flow through the passageway within camshaft support shaft 172 through the intake push rod tube 160 and into the valve chamber 156. When the piston rises, the crankcase pressure drops below atmospheric pressure. When the piston is raised, the A port is closed and the B port is opened enabling the pressurized air from valve chamber 156 to return to oil reservoir 158.

Of course, other means for inducing the circulation of misladened air from the oil reservoir to the valve chamber can be used to obtain the same function, such as check valves or alternative mechanically operated valve designs.

Having a loop type flow path as opposed to a single bidirectional flow path, as in the case of the embodiment of Figures 5 and 6 of our earlier application 52279/96, more dependable supply of oil can be delivered to the valve chamber.

It is believed that small lightweight fourcycle engines made in accordance with the present invention will be particularly suited to use with rotary line trimmers, as illustrated in Figure 1. Rotary line trimmers are typically directly driven. It is therefore desirable to have an engine with a torque peak in the 7000 to 9000 RPM range which is the range in which common line trimmers most efficiently cut. As illustrated in Figure 6 a small four-cycle engine of the present invention can be easily tuned to have a torque peak corresponding to the optimum cutting speed of a line trimmer head. This enables smaller horsepower engine to be utilized to achieve the same cutting performance as compared to a higher horse power twocycle engine which is direct drive operated. Of course, a two-cycle engine speed can be matched to the optimum performance speed of the cutting head by using a gear reduction, however, this unnecessarily adds cost, weight and complexity to a line trimmer.

Another advantage to the four-cycle engine for use in a line trimmer is illustrated with reference to Figures 7 and 8. Figure 7 plots the starter rope pull force versus engine revolutions. The force pulses occur every other revolution due to the four-cycle nature of the engine. A two-cycle engine as illustrated in Figure 8 has force pulses every revolution. It is therefore much easier to pull start a four-cycle engine to reach a specific starting RPM since approximately half of the work needs to be expended by the operator.

Since every other revolution of a four-cycle engine constitutes a pumping loop where there is relatively little cylinder pressure, the operator pulling starter rope handle 174 (shown in Figure 1) is able to increase engine angular velocity during the pumping revolution so that proper starting speed and sufficient engine momentum can be more easily achieved. The pull starter 20 mechanism utilized with the four-cycle engine is of a conventional design. Preferably, the pull starter will be located on the side of the engine closest to the handle in order to reduce the axial spacing between trimmer handle 24 and the starter rope handle 174, thereby minimizing the momentum exerted on the line trimmer during start up. A four-cycle engine is particularly advantageous in line trimmers where in the event the engine were to be shut off when the operator is carrying the trimmer, the operator can simply restart the engine by pulling the rope handle 174 with one hand and holding the trimmer handle 24 with the other. The reduced pull force makes it relatively easy to restart the engine without placing the trimmer on the ground or restraining the cutting head, as is frequently done with two-cycle line trimmers.

-11- It should be understood, of course, that while the invention herein shown and described constitutes a preferred embodiment of the invention, it is not intended to illustrate all possible variations thereof.

Alternative structures may be created by one of ordinary skill in the art without departing from the spirit and scope of the invention described in the following claims.

Throughout this specification and claims which follow, S unless the context requires otherwise, the word "comprise", and .9i variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers.

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Claims (10)

1. A four-cycle internal combustion engine comprising: an engine block defining a cylindrical bore, a cylinder head, a piston mounted for reciprocation in said cylindrical bore, said cylinder head defining a combustion chamber; an air-fuel mixture intake port and an exhaust gas port defined in said cylinder head assembly; a valve cover on said cylinder head defining a valve chamber; ge "intake and exhaust valves mounted in said intake and C exhaust ports, respectively, for reciprocation between port- open and port-closed positions; a valve-actuating valve train, said valve train 5h including at least one rocker arm and at least one valve See train push rod assembly extending at one end thereof within said valve chamber and engaging said rocker arm; ~a crankshaft rotatably mounted in said engine block including a crank position and a counterweight; 20 a connecting rod assembly having at one end thereof oeo... articulated connections to said piston and at the opposite o end thereof to said crank portion thereby forming a piston- oooo• connecting rod crankshaft assembly; a cam rotatably driven by said crankshaft and driven at one-half crankshaft speed, the opposite ends of said push rod assembly being drivably connected to said cam whereby said push rod assembly is actuated with a reciprocating motion upon rotation of said cam; said cylindrical bore, said crankshaft and said cam being located in a common plane; an oil reservoir; an oil mist generator element connected drivably to said crankshaft to engage the lubrication oil in order to create an oil mist in said reservoir which lubricates moving parts within the engine block, said reservoir being in fluid communication with said cylindrical bore whereby pressure P:\OPER\RSH\819687-98 spe 123.dc-19 Oobf, 2000 -13- within the oil reservoir fluctuates as the piston reciprocates; passageways extending between said reservoir and said valve chamber, to allow the flow of said oil mist through said passages to lubricate the valve train; and a flow control means providing an oil mist flow path from said reservoir to said valve chamber through said engine block and from said valve chamber to said reservoir and controlling the flow of said oil mist through said passageways to and from said valve chamber whereby oil mist is circulated through said engine, the flow control means !i~i being connected to act in synchronisation with increases and decreases in gas pressure in said engine block below said piston as said piston reciprocates in said cylindrical bore.

2. An engine as claimed in claim 1 wherein said driving connection between said cam and said crankshaft comprises a cam gear driven by said crankshaft, said flow control means e including said cam gear, a port in said cam gear registering 20 with one of said passageways whereby said one passageway is "alternatively opened and closed during revolution of said cam.

3. An engine as claimed in any one of the preceding claims including at least one push rod guide tube extending from said engine block to said cylinder head, a push rod extending through said push rod guide tube; in which said guide tube engine block and cylinder head forming a closed oil mist passage.

4. An engine as claimed in any one of the preceding claims wherein said oil mist generator element is integrally attached to said opposite end of said connecting rod.

PAOPERMRSH0 1987-98 se 125.doc.9 May, 2000 -14- An engine as claimed in any one of the preceding claims in which the valve-actuating valve train includes a pair of rocker arms and a pair of push rod assemblies.

6. The engine as claimed in any one of the preceding claims wherein said oil mist flow path extends through said engine in order to lubricate said intake and exhaust valves, said valve train, said crankshaft, said piston, and said cam. .9 *o

7. The engine as claimed in any one of the preceding *claims wherein said intake and exhaust ports are disposed in said cylinder head at spaced locations in said combustion chamber and a spark plug opening disposed generally 15 intermediate said intake and exhaust ports whereby an air fuel mixture is induced into said combustion chamber in a cross flow fashion, and near stoichiometric combustion may be maintained at standard operating conditions throughout a wide range of throttle settings. S

8. The engine as claimed in any one of the preceding *claims in which the displacement of the engine is 80cc or S9 less.

9. A method for lubricating a four-cycle internal combustion engine the engine having an engine block, a reciprocating piston in a cylindrical bore in the engine block, a crankshaft, a cam, a cam gear, a valve actuating valve train, a pair of rocker arms, an oil reservoir and a cylindrical head having a valve cover defining a valve chamber and intake and exhaust valves, the method comprising the steps of: creating within said oil reservoir an oil mist; providing said oil mist to lubricate said piston, PA\OPERRSH8196S7-98 sp 125.doc-19 Octobff. 2000 said crankshaft, said cam, said cam gear, said pair of rocker arms; the oil mist being further provided to said valve train, said intake and exhaust valves by conducting the oil mist through a passage from said reservoir to the valve chamber and conducting the oil mist in a return flow passage through said engine block from said valve chamber to said reservoir; and controlling the flow of oil mist from said reservoir to S 10 said valve chamber in synchronism with increases and decreases in gas pressure in said engine block below said piston as said piston reciprocates in said cylindrical bore whereby oil mist is distributed to said valve chamber throughout a range of angular orientations of the engine S 15 relative to vertical disposition of said cylindrical bore.

10. A portable hand held power tool having an engine according to any one of claims 1 to 8. DATED this 1 9 t h day of October, 2000 RYOBI OUTDOOR PRODUCTS, INC. By its Patent Attorneys: DAVIES COLLISON CAVE