CA1181348A - Economical engine construction - Google Patents

Abstract

ABSTRACT
An improved engine construction is disclosed having a valve train including valves and corresponding valve stems for controlling the intake and exhaust ports, cams for imparting reciprocating motion to the valves by way of the valve train, and a valve spring for biasing each valve toward its closed position and the valve train into tracking relation with the cam. The only element of the valve train coupling a cam to a stem is a cam follower with a depression for receiving the corresponding stem end and a cam engaging surface opposite the depression with the cam follower being held captive intermediate the stem and cam solely by the spring biasing of the stem toward the cam and the engagement of the stem end and the depression. The spring biasing is provided by a coiled wire spring having outwardly extending legs each of which engages a corresponding stem to urge the valves toward their closed position. The bight or coiled portion of the spring is held in a relatively fixed position by a portion of the engine casting. Another feature of the engine resides in the engine block casting which includes an exhaust gas passageway extending from an engine cylinder and including near the end thereof remote from the cylinder an enlarged cavity which defines at least a part of a muffler shell. Numerous other elements may be cast integral with the engine block including a boss for attaching a pull rope recoil starter assembly along with an anchoring point for one end of the rewind spring of that starter assembly and retaining guides for the rope of the starter assembly. The locator, such as a stud for the intake and exhaust poppet valve biasing spring, may also be cast integrally with the engine block. A further feature of the engine resides in a combination crankcase breather mechanism and oil fill cap which due to its remote location from the engine crankshaft as well as the tortuous air flow path through the cap to the atmosphere minimizes the egress of oil from the engine through the breather mechanism.

Description

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The present inven-tlon relates generally to small internal combustion engines of the type which might for example be employed in snowthrowers, lawnmowers and the like, and more particularly ,to such an enyine incorpo,ra-ting several innovative techniques to reduce the overall cost of manu-facture of that engine.
This is a division of copending Canadian Patent Application Serial No, 378,146, filed May 22, 1981.
Engines of this general type are frequently vertical crankshaft four-stroke cycle engines provided with a powered take-off shaft for example to drive the wheels of a self-propelled lawnmower having but a single cylinder, a solid state ignition arrangement and a pull rope recoil star-ter.
Such eng~nes have been well known for a number of years and have met with conside~able commercial success and ~hile the present inyention w111 be described i~rl the context of such an engine~ the i~nyenti~on is clearly applicable to other engine des~i~gns.
Engines of the type descri~ed are not without their problem,s and one eyer present requirement i~n the design of such- engines is the minimization of manufacturing costs. For exa,mple, t,he yalye train typically found in such engines em,ploys a number o~ spur gears coupli~ng the engine crankshaft to one, ~r m,ore cam shafts to properly ti~e the opening and closillg of the intake and exhaust ports. ?hese spur years a~e,~etallic and generally expens~ve to manufacture si`nce they~requI~re accurate machining of the gear teeth.
The asse,mkly of the yalve train i~s als~ a tIme consuming operating inyolving the simultaneous positioning of the , valves in their seats and respective yalYe stems in their gu;`des and the positionin~ o,f the valve lifters'in their respect:ive guides~ as well as the engaging of generally mab/~

complex spring biasing arrangernents, to hold these several elements in position and bias the valves toward their closed position. One improvement in this complicated assembly procedure is illustrated in ~nited States Patent No.
3,556,062 assigned to the assignee of the present invention.
In that improvement patent, a single split loop or hairpin type valve spring ~i~ases both the intake and exhaust val.ves toward their closed position, however, that arranyement still employs yalye lifters and the associated li~fter guide arrangement, making assembly somewhat more difficult than necessary, as will be apparent in the sequel.

One part;cularly annoying problem with engines of the type described, and indeed with most internal combusti~on engi~ne arrangements, involves the rusting out and/or falling o~f of the engine exhaust muffler~ With engines of the type described, mufflers form,ed of stamped sheet metal ~equir~i~ng a subse~uent cri~pin~ operation, are fastened:bo the engine block by a pair of bolts. Dlle to mass of -the muffler and yibration, these bolts frequently loosen, allow-ing exhaust ga erosi~on to occur where the muffler attaches to the block, and frequently resulti~ng in the loss of the ~uffler, .~Further, th.e stamped sheet metal muffler itself, due to tem,perature and moi$ture buildup, eventually falls y~i~cti~.to rusting and exhaust ~as erosion. Accordingly, th.e~proyision:o~.a muff~e~ arrangement less subiect to rust and erosi~n wi~th.better retention on the engine, would be hi~hly desi~rable.

Accordin~ to the present invention~ there is pro-vided an arrangement for biasing intake and exhaus-t poppet - valYes toward their closed positions includi~ng a coiled wire spring having a pair oE outwardly extending legs with each leg connected to one of the respective valves. The central bight portion of this coiled wire spring is anchored, such mab/; Y

~8~ 8 as by a stud relatively fixed in a location intermediate ~the valves and passing through the coïl of the spring so that the stud and one valve provide the fixed support points against which the spring is flexed when the other valve opens.
Referring now to the accompanying ~rawings:--Fig. 1 is a perspective view of a low cost internalcombustion engine incorporating the several features of the present invention;
Fig. 2 is a cross-sectional view of a portion of the block of the engine of Fig. 1 showing the formation of the muffler shell therein;
Fig. 3 is a view in elevation of one of the like pair of apertured metal ~affle plates which occupy the open end of the muffler shell defining cavity of Fig.

2;
Fig. 4 is a view partially in section and at a right angle to the yiew of Fig. 2 lllustrat;'ng a pOrtIon o~ the engine block casting including the intake and exhaust valye seat and the integrally cast muffler shell;
Fig. 5 is a ~i~ew in section along the line mab/ ~

1 5-5 o~ Fi~. 1 illus krating the engl.ne vAlve kr~in;
~ig 6a and 6~ illustrate the valve stem an~
ca~ ~ollower of ~ig. 5 with the section o~ the follower in Fig, 6a bein~ along the lines 6-6 of ~ig 6b;
- Fig. 7 il~us~rates a pull rope recoil starter disposed on tha engine of ~ig~ 1 on the si~e opposite ~he cylinaer head and spark plug;
Fig. 8 is a v~ew of the auxiliary po~er ~ke-off ~rrangement and-a portion o the valve ~rain as seen from ~he riyht o~ ~ig. 5j FigO ~ is a sectional ~iew along the line 9-9 o~' ~ig.. ~
Fig. 10 is a view in cross-section al~g the line 10-10 of Figs. 1 ~nd 5 illustr~t:ing the engine crankshaft and recoil start ~echanism; and ~ig.- 11 is a view i~ section alony line 11-11 0~ FigO 1 illustrating the combined cra~kcase . brea~h~r ana filler c~p~ . . - -Corresponding reference charac~ers in~cate corresponding par~s throughouk the several ~iews o.~ ~he ~r~wing~
. The exemplificat.ions set ou~ herein il~ustra~e a preferrea embodinent o~ the invention in ~ne 25 ~orm ~hexeof and such exemplifications are n~ .
t~ ~e construed as limiting the scope of ~he disclosiure ox the scope of the invention in any ~anner_ ~eferring first to some of the broadl~ conventio~a~
features of the intexnal combustion engine 13 of ~ig~ 1, in operation a.ir is inyested throug~ air cleaner 15 to be mixed with fuel in carbure~or 17, and ~hat ~uel air mixtu.re passing throug~ an - inta~e conduit past the oen -ntake valve 21 o~
.
.the poppe~ or lift variety (~ig. 5) ana into cylinder 23 ~Fiy. ~ to be cor~pxessed ana ignited b~r a spar~
~rom sparkplug ~, i.nitiating the expansion or _ g _ . . I

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1 power stroke oE the plston. Therea~ter, valve 21 remains closed and exhaust valve 27 (~;y. 53 opens and as the piston progresses toward cylinder head 29, the exhaust gases are expelled from the ~ cylinder hy way of e~haust port 31 [~ig. 5) ana the exhaust muffler 33 to the atmosohere.
Referring briefly to Fig. 10, the engine piston is connected ~y a conventional connecting rod 35 to crankshaft 37; the lower end of which may connect ~o a mower blade in known fashi-on. The upper end of crànkshaft 37 is connectea to a ~lywheel 39 which may have a pluralit~ of vanes 41 and 43 for circulating air within an engine housing, not shown, for the purposes of illustration, as well as a toothed gear portion 45 for cooperating with ~eeth on a spur gear 47, se~ectively actuable by a pull rope to engage the keeth 45 to start the engine, and additionally may include a permanent magnet or othex portion of an ignition system for the engine. Flywheel 39, as suchh ~ay be of the ~y~e disclosed in U.S. Patent No. 4,278,054, issued July 14, 1981, and assigned to the assignee o~ the present application, ~hile the engine ignition system is not il~ustrated, but may ~e of the type illustrated in either U.S.
Patent 3,490,426 or 3,952,712, as well as an~ of several other known ignition systems with the ~osses 49 and 51 of Fig~ 1 being provided to mou~ that ignition system.
Turnin~ now to some o the non-conventional features of the present in~ention, and xeferring still to the drawing generall~, it should first be notea th~t a number of the engine parts are manufactured as cast plastic parts while their prior art counterparts, if they exist at all, are manufactured of metal and have the earlier mentioned su~sequent expensive machining operation required.

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1 Thus, in FicJs. 5, 6, ~ and 9, the radial cams 51 and 53 and the s~ur dxive gears 55 and 57, along with spur gear 59, power take-off bevel gears 61 and 63, and the pair of cam followers or shoes 5 - 65 and. 67 may all be manufactured from a plastic material, ho~Jever, in many cases some of these elements, such as spur gear 59, may be of a powdered metal or other type material. In one embodiment of the pre~ent invention~ the cams and spur drive gears ~nd bevel gear 63 were injection mol~ed of Dupont' s ZYTEL 70G33HSl while the Iifters 65 were in~ection molded of Dupon-tls DELRIN 100 NC-10.
Another difference in the design philosophy of the.present engine, as co~pared to known prior art engines, resides in the casting of the engine block with a number o~ auxiliary elements in~egrally cast therewith and this in.tegral casting feature is facilitated somewhat by locating ~he parting plane 6g substantially higher than on prior engines.
20 . Typically, the partin~ plane for the block cas~-ing on pxior engines is located close to the power take-off shaft 71. Thus, the spring ~ocating stud 73, a lug 75 for anchoring one end of the pull rope recoil starter spring, a pull rope guide 77 J
the boss 79 for mounting the pull rope recoil starier, and the previously mentioned exhaust mu~fler shell 33 may all be cast as an integral part of the engine block rather than fabricating each of these devices as a separate part which must be fastened to the - 30 block, requiring additional labor and increased cos~s .
Delvin~ moxe deeply into the unique aspects of ~he present invention, and referrin~ irst to Fig. 6, the valve portion 27 may be of any conventional poppet or lift ~alve con:Eiguration, typically having a tapered seat portion for mating with a s;milarly tapered seat portion 81 of the engine exhaust port * - Trade Marks of Fi~s. ~ an~ 5. The in-take port will have a similar tapered sea-t portion 83 Eor mating with the intake valve.
Stem portion 85 is provided with a notch 87 for engagernent with the leg 89 of the spring, and leg 97 engages a similar notch in the intake valve stem so that the spring biases both valves toward their closed position. Stem end 91 which is the end of the stem opposite the valve 27 fits snugly within the depression 93 of the canl follower or shoe 65 and of course the surface 95 opposite this depression in thè
shoe is the surface which rides on the surface of~radial cam 51. It will be noted that when notch 87 is engaged by the spring leg 89, rotation of the valve about the stem axis will be prevented.
The above described valve structure utilizing the cam follower 93 is also disclosed and is claimed in above-identified parent application Serial No. 37~ 6.
The exhaust valve and cam follower of Fig. 6 is illustrated in position within the engine in Fig. 5 along with a very similar intake Yalve 21 and cam follower or shoe ~o 67. Both valves are biased toward their closed position by the legs 89 and 97 of the coiled wire spring engaging their respective stem notches with the bight or helical portion 99 of this spring being held in a relatively fixed location by the stud or boss 73. It would, of courser also be poss-i~le to form a pocket in the engine block casting for holding this bight portion in posi`tion. Thus, each valye s-tem notch provides a ~ixed support for one sprin~ leg when the other valve opens, flexing the spring. That this support location be fixed is of course not necessary, however! since i~ntake and exhaust valves are typi~cally not open at the same time ! the support location is fixed relatiye to the other valye when that other valYe opens. It should also be noted that no valve lifter guides are employed in the mab/j~c, 3~

1 present engine and that the cam followers 65 and 67 are held in position solely by the valve stem engagemen~ ~ith the depression in the follower and the sprlng urging of the stem toward the cam S so that the cam follower is captive between the cam and valve stem.
Stil~ ref~rring to Fig. 5, it will be noted that the gears 55 and 57 have a like number.of teeth with this n~mber being twice the n~mber of lQ teeth on spur gear 59 so that for each rotation of the spur gear 59, each of the gears 55 and 57 executes one-half revolution~ The gear S9 is directly driven by the engine crankshaft 37 ~hereby pxoviding the desir~d opening and closing of each o~ the lS intake an~ exhaust valves once during two revolutions of the engine.
A bevel gear 63 engages a su~stantially smaller bevel gear 61 on the rear 5ide of spur gear S7 r as best seen in Figs. 8 and 9, with this substantial disparity in bevel gear sizes, an~ the two:one speed re~uction between gears 59 and 57 providing the desired low speed rotation of the power ta~e-off shaft 71, as for example will be desired to drive th~ wheels of a power lawnmo~er. Gear 55 may be i~entical to gear 57 including the bevel gear port~on like ~1 t if the reduction in .initial tooling ~sts as well as the reduction in requixed spare par~s inventory justifies this duplication, or gear 55 may be of a more simplistic design, since it need only drive cam 51. Of course also, somewhat di~ferent engine conf.igurations may allow cams 51 ~d 53 to share a common shaftO
Figs. 2, 3, 4 and 5 illustrate the integrally cast mu~er shell of the present invention. As perhaps ~st seen in Figs. 2l 4 and 5, an exhaust gas passageway 31 extends from the enyine c~li.nder 13~
/
1 23 by wa~ nf the exhaust port between valve 27 and seat 81 passing into a substantially enlarged area or cavity as deflned by the shell 33 which forms at least a part of the muffler shell~ Within S ~he cavity and terminating near the open end, there is located a boss 101 also cast as an integral portion of the engine block and having an outwardly *acing hole 103 which may be tapped or which may simply be a cast hole for receiving a self-tapping or self-threading screw 105~ In either case, the boss provides a support for the muffler baf~les 107 and 109.
As best illustrated in Figs. ~ and 3, each ba~le comprises an ayertured meta~ plate ~or providing a circuitous or ~ortuous exhaust path from the cavity to the atmosphere. In Fig. 2, as illust.rated by the a~rows, this path from exhaust p~ssageway 31, is through the apertures near the bottom of plate 101~ ~hen upwardly between the two plates and outwardly through the apertures ~n the upper por~ion of plate 1070 The plates may be substantlally iden~ica~, each having a generally centrally located depression 111 with the attachment ~olt passing aperture 113 within the depresslon. The plates are positioned with their respective depressions abutting and the remaining plate portions separated by about t~ice the depth of the depressions and with bolt lOS passing through the respective apertures such as 113 and into hoss 101 to securely hold the platés in position near the cavity open end.
As most clearly shown .in.Fig. 3, each plate is of a gene.r~lly rectangular configuration provided with a plurality of small exhaust gas apertures, such as 115 and 117, with those small apertures being concentrated in one half of the rectangular 3~

1. configuration wh.ile the other half thexeof is substantially aperture free. When the plates are then positioned with depression against depression-, the apertured half of plate 107 is near the top, as illustrated in Fig. 2, while the apertured half of plate 109 i5 near the bottom of that same Figure~
~ he combination crankcase breather mechanism and oil fill cap 119 of Fig. 1 functions to restrict an oil filler opening in the engi~e which communicates ~y way o~ an ~il fill tube ~enerally at 121 and leading to the engine oil sump 123 (Fig. 10) while pro~iding a flow path for the expulsion o~ gases from the engine crankcase 125 (Fig. 10) and limiting the egress ~ oil from the engine through that flow pat~. This breather mechanism cap combinatio~
~s illustrated in cross-section in Fig. 11 and inclu~es a screw cap portion 127, an u~pex baffle por~ion ~29, and a lower baffle portion 131, all fastened ~ogether to provide a circuitous path, as-illustrated by the arrows, ~rom the cxank~ase to the atmosphere, by way of the disc 133 of a check valva and an oil colle~ting tray 135 ha~ing oil retur~ arain holes, ~uch as 137, near the bottom thereof~ .
Referr;ng to Fig. 11 in greater detail, the oil ~ill opening may have a neck 139 with a threaded region 141 which engages a complementaxy portion of the screw cap 127 about the oil fill openin~.
The upper baffle poxtion 1~9 has a downwardly depending generally cylindrical baffle 143 while the lower baffle.portion 131 has inner 145 and outer 147 generally cylindrical baffles which are interleaved with th ~ownwardl~ depending baffle 143. The disc 133 of the check valve is cap~ive with a limited amount of free movement between the upper ~ld lower b~ffle portions. This check valve restricts the 1 entrance oE air into the engine crankcase by way of the breather mechanism ~7hile allowing the expulsion - of gases rom ~he ~ngine crankcase by way of the breather ~echanism. The expulsion gases pass, as indicated by the arrows, upwardly through the check valve and over an uppex rim of the inner lower baf1e 145 ~nd then downwardly between the baffle and the downwardly depending baffle l43 and beneath a lower rim or edge of baffle 143 to ~hen pass upwaxdly between the outer lower baffle 147 and the ao~mwar~ly depending baffle 143, through a plurality of cap apertures, such as 149, 151 and -155 to the atmosphere. I.rhe inner cylindrical baffle 145~ of course, includes a valve seat lS3 of an annular con~iguration while the downwardl~
dependlng cylindrical portion 156 of the upper - baffle p~r~ion restricts ~he ~alve disc to move-ment within the inner cylindrical baffle. An oil collecting kxay of an annular configuration is formed by the bottom portlon 1~7 which connects the inner and outer baffles from whichr as noted earlier, oil drains back to the engine sump by way o~ drain holes, such as 137. It should also be noted that the location of the cap 119 ~emote from and sùbstantially above the engine sump oil level 7 aids materially in the se~aration of oi.l from the escaping gases, as those gases pass along the oil fill tube extending from the engine crankcase to the oil filler opening~
Referring now to Figs. 7 and 10, pulling ~he start handle 159 causes rope 161 to unwind from the drum ~63~ inducing rotation in that drum and helically threaded hub 167 about the axis of the recoil starter attaching bolt 165 and inducing a restorative force in the starter recoil spring.
Gear 47 is attached to the hub 167 of the startex 31'1~13~3 1 mechanis~ by a helical thread arrangement so that rotation of drum 163 causes gear 47 to move toward the left, as viewed in Fig~ 10 and into engagement with the ~eeth 45 of the fl~wheel with continued S ro~a~ion of hub 163 and of gear 47 providing the starting rotation of the flywheel. Spring clip 168 fric~ionally engages hub 167 and spans stud 75 to move the hub and startoer gear between their axial limits. When the engine starts, gear 47 is disengaged and release of the handle 159 allows the mechanism to rewind for the next starting operation since ~he clock type coil spring urges the gear 47 back alony the helical thread arrangement, and as tension of rope 161 is released, that rope is rewound about the drum 163. The further details o the s~arter mechanism may be as in conventionally ~mployea re~Jind starters, as illustrated in U.SO
Patent 3,375,813 for example, however, as noted earlier, substantial economies in the manufacture 20 of the engine are realized by casting the recoil starter attachment boss 79 as well as the spring anchoring stud 75 and recoil starter xope guide 77 as integral portion5 of the engine block~ and eliminat~ng all support bxackets. Another suitable recoil s~arter is illustrate~ in U.S.~Patent 4,019,490O
~ro~ the fore~oing, it is now apparent that a nov~l interna~ combustion engine having a unique block casting and valve train arrangement, as well as unique muffler and breather configurat;ons,-has b2en disclosed meeting the objects and advantageous features set out hereinbefore as well as others and that modifications as to the precise configurations, ~ shapes and details may be made by those having ordinary skill in the art without departin~ from the spirit of the in~ention or the scope thereof as set o~t by the claims which follo~.

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An arrangement for biasing intake and exhaust poppet valves toward their closed positions including a coiled wire spring having a pair of outwardly extending legs with each leg connected to one of the respective valves, and a stud relatively fixed in a location intermediate the valves and passing through the coil of the spring whereby the stud and one valve provide the fixed support points against which the spring is flexed when the other valve opens.

2. In an internal combustion engine having a valve train including a pair of stems and valves connected to each of the stems for controlling intake and exhaust ports respectively of the engine, cams for imparting reciprocating opening motion to each valve by way of the valve train, and a spring for biasing the valves closed and the valve train into tracking relation with the cams, the improvement wherein the spring comprises a coiled wire spring having an anchored central bight portion and outwardly extending legs, each engaging one of the pair of stems to urge the respective valves toward a closed position.

3. The improvement of claim 2 wherein the central bight portion is anchored by a stud fixed to the engine and about which the bight is positioned,

4. The improvement of claim 2 further comprising a guide-free cam follower captive intermediate a stem and corresponding cam.

5. The improvement of claim 2 wherein the cam follower comprises a non-metallic shoe having a depression for receiving a stem end opposite the corresponding valve and a cam engaging surface opposite the depression.

6. The improvement of claim 5 wherein a non-metallic shoe is provided intermediate each stem and corres-ponding cam.

7. The improvement of claim 2 wherein the spring legs engage the respective stems in a manner to prevent stem rotation about the axis of reciprocating motion.

8. The improvement of claim 2 wherein the cams for imparting reciprocating motion comprise a pair of non-metallic radial cam surfaces shaft driven by a like pair of non-metallic spur gears.

9. The improvement of claim 8 wherein the cams are driven by a common spur gear fixed to the crankshaft of the engine which gear meshes with each of the like pair of gears.

10. The improvement of claim 9 further including a power take-off shaft and a pair of meshing non-metallic bevel gears, a smaller of which is fixed to one of the cam surface shafts for rotation therewith and a larger of which is fixed to the power take-off shaft.