CA1261695A - Automatic compression releasing device for four-cycle engine - Google Patents
Automatic compression releasing device for four-cycle engineInfo
- Publication number
- CA1261695A CA1261695A CA000498400A CA498400A CA1261695A CA 1261695 A CA1261695 A CA 1261695A CA 000498400 A CA000498400 A CA 000498400A CA 498400 A CA498400 A CA 498400A CA 1261695 A CA1261695 A CA 1261695A
- Authority
- CA
- Canada
- Prior art keywords
- moving member
- tappet
- cam
- force
- gear
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B75/00—Other engines
- F02B75/02—Engines characterised by their cycles, e.g. six-stroke
- F02B2075/022—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle
- F02B2075/027—Engines characterised by their cycles, e.g. six-stroke having less than six strokes per cycle four
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- Valve Device For Special Equipments (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An automatic compression releasing device intended for reducing the pressure inside the combustion chamber of the four cycle engine at the start by opening and closing the intake or exhaust valve of the combustion chamber actuated by the cam on the cam shaft through the tappet. A single moving piece mounted, on the side of the gear integrated with the cam shaft, as enclosing the cam shaft, can slide over the side of the gear in a given direc-tion, guided by two slots opened in the moving piece and two pins planted on the gear side. A tappet lifting arm is extended from the moving piece to such a position as to push up the tappet. At the start, the centrifugal force on the moving piece is designed not to exceed the opposing force, thus keeping the tappet lifting arm projected out of the cam base circle, and also retaining the returning force of the moving piece acting on the tappet lifting arm through the tappet being supported by the guide slots and pins. During the normal rpm, the centrifugal force on the moving piece overcomes aforesaid opposing force to slide the moving piece along said guide slots, bringing the tappet lifting arm level with or further down into the cam base circle.
An automatic compression releasing device intended for reducing the pressure inside the combustion chamber of the four cycle engine at the start by opening and closing the intake or exhaust valve of the combustion chamber actuated by the cam on the cam shaft through the tappet. A single moving piece mounted, on the side of the gear integrated with the cam shaft, as enclosing the cam shaft, can slide over the side of the gear in a given direc-tion, guided by two slots opened in the moving piece and two pins planted on the gear side. A tappet lifting arm is extended from the moving piece to such a position as to push up the tappet. At the start, the centrifugal force on the moving piece is designed not to exceed the opposing force, thus keeping the tappet lifting arm projected out of the cam base circle, and also retaining the returning force of the moving piece acting on the tappet lifting arm through the tappet being supported by the guide slots and pins. During the normal rpm, the centrifugal force on the moving piece overcomes aforesaid opposing force to slide the moving piece along said guide slots, bringing the tappet lifting arm level with or further down into the cam base circle.
Description
:~26~
AUTOMATIC COMPRESSION RELEASING DEVICE
FOR FOUR-CYCLE ENGINE
Field of the Invention and Related ArtStatemen-t This invention relates to an automatic compression releasing device for reducing the compression pressure of the gas mixture in a combustion chamber by automatically opening the inlet or exhaust valv~ slightly in starting an engine, thus leading the starting torquè of the general-purpose four stroke cycle engine to be minimized for eash start.
In gen~ral, since a large forcc must be applied to start the general-purpose four-cycle engines, especially for large sized ones, by means oE manually driving -the recoil starter, reducti.on in the torque required Eor star-ting has been eagerly demanded la-tely. To comply with this require-ment, the automtic compression re:Leasing devices have been developed for practical use, which can lower the compression pressure of gas mixture inside the combustion chamber for a less starting torque by automatically opening the intake or exhaust valve slightly in starting, and to automatically release its function after the ~nglne has come up to a preset speed of rotation.
The type of the automatic compression releasing device according to the prior art, and as disclosed later in the description, necessitates accuracy in parts dimensions and their assembly because of the presence of more than one moving members actuated by centrifugal force, and also has a complicated structure, leading to high cost. It also requires '." ~3~ ' 1 ~.
:~6~6~
two moving members which introduce a serious drawback of large irregularities in the frictional resistances between -~~
the moving members, and the pins and the gear side faces on which said moving members slide, as well as in the viscous resistance of oil, resul-ting in the unstability of the preset rpm to remove the compression releasing action.
Object and Summary of.the Inven-tion -It can be said that the purpose and object of this invention is -to provide an automatic compression releasing device for the four-cycle engine, which is simple ln cons-truc-tion, dependable in func-tion, easy in assembly and steady in operat.ion, thus e.l.i.m:inat:ing thc drawbacks of the pri.or art.
To achleve this object, an automatlc compresslon releaslng devlce for reducing the gas pressure ln a combustion chamber of a four-cycle englne for use ln startlng the four-cycle englne ln whlch lntake and exhausk valves are opened and closed by reciprocating tappets by means of the rota-tion of a cam on a cam shaft through its rota-tion. The devlce comprises a slngle moving member disposed on a side of a gear integrated with -the cam shaf-t in such a way as to surround the cam shaft. A tappet-lif-ting arm is extended from the moving member to a position where i-t can push up a -tappet in a compression stroke of the engine. Two guide slots are bored in the moving member, and two pins are planted in the gear so as to engage with the respective slots, where the engagement of the pins with the slo-ts allows the moving member to slide independently along with the slde of the gear ln a predeter-
AUTOMATIC COMPRESSION RELEASING DEVICE
FOR FOUR-CYCLE ENGINE
Field of the Invention and Related ArtStatemen-t This invention relates to an automatic compression releasing device for reducing the compression pressure of the gas mixture in a combustion chamber by automatically opening the inlet or exhaust valv~ slightly in starting an engine, thus leading the starting torquè of the general-purpose four stroke cycle engine to be minimized for eash start.
In gen~ral, since a large forcc must be applied to start the general-purpose four-cycle engines, especially for large sized ones, by means oE manually driving -the recoil starter, reducti.on in the torque required Eor star-ting has been eagerly demanded la-tely. To comply with this require-ment, the automtic compression re:Leasing devices have been developed for practical use, which can lower the compression pressure of gas mixture inside the combustion chamber for a less starting torque by automatically opening the intake or exhaust valve slightly in starting, and to automatically release its function after the ~nglne has come up to a preset speed of rotation.
The type of the automatic compression releasing device according to the prior art, and as disclosed later in the description, necessitates accuracy in parts dimensions and their assembly because of the presence of more than one moving members actuated by centrifugal force, and also has a complicated structure, leading to high cost. It also requires '." ~3~ ' 1 ~.
:~6~6~
two moving members which introduce a serious drawback of large irregularities in the frictional resistances between -~~
the moving members, and the pins and the gear side faces on which said moving members slide, as well as in the viscous resistance of oil, resul-ting in the unstability of the preset rpm to remove the compression releasing action.
Object and Summary of.the Inven-tion -It can be said that the purpose and object of this invention is -to provide an automatic compression releasing device for the four-cycle engine, which is simple ln cons-truc-tion, dependable in func-tion, easy in assembly and steady in operat.ion, thus e.l.i.m:inat:ing thc drawbacks of the pri.or art.
To achleve this object, an automatlc compresslon releaslng devlce for reducing the gas pressure ln a combustion chamber of a four-cycle englne for use ln startlng the four-cycle englne ln whlch lntake and exhausk valves are opened and closed by reciprocating tappets by means of the rota-tion of a cam on a cam shaft through its rota-tion. The devlce comprises a slngle moving member disposed on a side of a gear integrated with -the cam shaf-t in such a way as to surround the cam shaft. A tappet-lif-ting arm is extended from the moving member to a position where i-t can push up a -tappet in a compression stroke of the engine. Two guide slots are bored in the moving member, and two pins are planted in the gear so as to engage with the respective slots, where the engagement of the pins with the slo-ts allows the moving member to slide independently along with the slde of the gear ln a predeter-
- 2 -mined direction. In the cranking stage, a centrifugal force acting on the moving member in parallel with the rotation speed is designed not to overcome a force acting on the moving member against the centrifugal force, resulting in the moving member being so retained at a position that a face of the tappet-lifting arm is kept as projecting outside a base circle of the cam, and a returning force of the moving member acts on the tappet-lifting arm through the tappet and being able to be sustained by the combination of the slots and the pins.
The force acting on the moving member against the centrifugal force consis-ts of the force of gravi-ty to the moving member and a Erictional force between -the guide slots and the pins.
In normal sp~eds, th~ c~ntrifugal Eorce on the moviny member induced by the rotation speed of -the engine is so designed to overcome the opposite force acting on the moving member so that the moving member moves to such a position that the fact of the tappet-lifting arm comes down level with or inward of the cam base cirle.
In the accompanying drawings, there are shown illus-trative embodiments of the invention from which these and other of its objectives, novel features and advantages will be readily apparent.
FIG. 1 is a front view of an embodiment for an automatic compression releasing device for the four-cycle engine in accordance with the invention;
FIG. 2 is a sectional view taken along line A-A in Fig. l;
FIG. 3 is a front view of the au-tomatic compression 6~i releasing device in Fig. 1 in the normal operating condition;
FIG. 4 is a front view of another embodiment of an automatic compression releasing device for the four-cycle engine in accordance with the invention;
FIG. 5 is a front view of the automatic compression releasing device in Fig. 4 in the normal operating condition;
FIGS. 6a through 6e are illustrations of the opera-tion of the embodiment shown in Fig. l; and FIG. 7 is a front view showing a typical type of the automatic compression releasing device for the four-cycle engine in accordance with the prlor art.
R~ferring Eirs-tly to Figur~ 7, which lllustra-tes th~ prior art o-E ~apanes~ Utllity Model No. 1~207C0 and enti-tled "Au-toma-tic compression Releasing oE Internal Combus-tion Engine", there is shown a typical example of the automatic compression releasing devices, and relating to the four-cycle engine in which the rotation of the cam shaft 1 causes the intake or exhaust valve 5 in the combustion chamber 4 to be opened or closed by reciprocating the tappet 3 through a combination of the cam 2 on the cam shaft 1 and the valve spring 34. The automatic compression releasing device com-prises an arcuate moving member 7 rotatably supported by a pin ~ approximately at its center on one half of a side face of the gear 6 integrated with the cam shaft 1 having the cam 2 actuating an either valve as described above; an arm 9 projecting sideways from one end of the inner circumference of the moving member 7 to push up the tappet 3; another arcuate moving member 10 ùisposed on the other half of the :i . .
1, _ ~ _ side face of the gear 6; one end of the member 10 rotatably supported by another pin 11 on one end of aforesaid moving member 7; the other end of the moving member 10 provided on its outer circumference with the guide 12 consisting of a plurality of semi-circle recesses to engage with the separa-te pin 1.3 attached on the side face of the gear 6; and a spring 14 extended between one point on said other end of the moving member 10 and the other point on the moving member 7 located on the side opposite to the pin 11 relative to the pin 8.
In the start while -the engine rpm is still low, the moving members 7 and 10 of the automatic compresslon releasing device are held ln place, since the spri.ng 14 is pulling the lower end of the moving member 7 close to the mov:ing member 10 against its then small centrifugal force. Since the arm 9 extended sidewards from the inner circumference of the moving member 7 then takes a position projecting out of the cam base circle 2, the arm 7 pushes up the tappet 3 in the compression stroke for every rotation of -the cam shaf-t 1 to slightly open the valve 5, thus letting out a par-t of compressed gas mixture resulting in a reduction of starting torque.
On the other hand, as the engine rpm comes up, since the moving members 7 and 10 swing outward respectively about the pins 8 and 11 due to their centrifugal forces over-coming the force of the spring 14, aforesaid arm 9 changes the position inwards of the base circle 2a of the cam 2, thus losing the function of pushing up the tappet 3, resulting in the valve 5 being intact in the compression stroke to have the normal closing function of the valve 5 following only the cam 2 on -the cam shaft 1.
6~
Referring now to the drawings depicting in detail embodimen-ts in accordance with the invention, Figs. 1 and 2 illustrate an embodiment of an automatic compression releasing device for the four-cycle engine. In these drawings, 1 is a cam shaft and 2 is a cam fitted on the cam shaft 1. Tappet 3 opens and closes an intake or exhaust valve 5 in a combustion chamber, which is reciprocated by the cam 2 and a valve spring 34. Gear 6 is mounted on the cam shaft 1 next to cam 2, and on the side of said gear 6 a moving member 20 is disposed surrounding about a half of the cam shaft 1. The moving member 20 is slidably supported outwards along the side of gear 6 by pins 23 and 24 planted in the side of gear 6 through an elllptlcal gulde slot 21 and an L-shaped gulde slo-t 22 which are .respect.ively bord sldeways ln the opposi.te slcles ~.n relation to th~ sha:Et c~nt~r.l.:i.n~ of the cam shaft .l. 'rhe movlng member 20 has an arrn 25 projectlng sldewards, ln order to llft the tappet 3 at least ln the compresslon stroke. In thls embodlment, a sprlng 27 ls so extended between the tappet llftlng arm 25 and a hole 26 drllled in the side of -the gear 6 that said tappet lifting arm 25 ls forced to project radlally out of the base clrcle 2a of the cam Z durlng the cranking perlod when the englne ls bei.ng started. The base clrcle 2a of the cam 2 ls partly removed ln order -tha-t the cutout can accommoda-te the protrudlng tappet llftlng arm 25.
In the embodlment of the automatlc compresslon releasing devlce according to the lnventlon as described abover while the engine is at rest, the movlng mernber 20 ls pulled by the sprlng 27 toward the hole 26, and also is helped by the engagement of . ~ - 6 -.. ........ j 6~
the pins 23 and 24 planted in the side of the gear 6 with the guide slots 21 and 22 so that the taPPet lifting arm 25 takes such a position out of the base circle of the cam as to effect the compression releasing function.
~'hen cranking the engine at the start, the moving member 20 receives a small centrifugal force corresPonding to the rotation speed of the cam shaft 1. But at this time, since the centrifugal force never exceeds the resultant force of the gravity to the moving member, a frictional force between the pin 24 and the guide slot ~2, and a tension of the sPring 27, the moYing member 20 has no relative movement to the gear 6, thus resulting in the tappet liftin~ arm 25 Proiecting out of the base circle 2a of the cam 2. Therefore, in the compression stroke, the tappet is raised by the tapPet lifting arm 25 while the moving member 20 being supported by the guide slot 22 and the pin 24, resulting in the Yalve 5 remaining oPen until near the top dead point of compres-sion stroke to allow the gas mixture to escape, thus minimizing the starting torque.
hs the engine reaches the normal operating condition gathe-ring speed, induced by the centrifugal force which has become greater than the resultant f orce of said graYitational f orce, f rictional f orce and pull of the spring 27, the moving member 20 begins to rotate around the pin 23, thus causing the pin 24 opposite to the pin 23 to move to the edge of the bent portion in the guide slot 22. Since from this po int both guide slots 22 and 21 have the same direction as shown in Fig.3, the moving member 20 begins to slide outwards (downwards) along the side of the gear 6. thus causing the tappet lifting arm 25 receding back into the cutout on the camshaft 1 or into the inside of the base circle 2a of the cam 2. resulting in the loss of the function to lift the valve 5. This enables the valve 5 to rcmain closed over 5 the compression stroke in accordance with the normal open-close function of the valve 5 controlled by the cam 2 on the camshaft 1.
When the eng;ne comes to a halt, since the centrifugal force generated on the moving member 20 by the rotation of the engine disaPPears. the moving member 20 is pulled back in place by the pull of the spring 27 as shown in Figs. 1 and 2 to restore the comPreSSion releasing function of the tappet lifting arm 25.
In this embodiment using the spring 27, the moving member 20 is so designed as to be forcibly returned in Place to regain the compression releasing function by the spring 27 when the engine comes to a halt. In the case of the common horizontal engine having the camshaft 1 in the direction perpendicular to that of the gravitational force, however. without the spring 27, the moving member 20 can be returned in place to restore the compres-sion releasing function just before pushing up the tappet 3,through the relative movement of the moving member 20 as shown in Fig.6a throu~h 6e, within the last one rotation of the camshaft 1. when the engine is going to a halt, while losing the centrifu-gal force on the moving member. That's because, in a front view of Fig.1, the gear 6 rotates anticlockwise, and both the slots 21 and 22 are opened diagonally from top right to bottom left. In Fig.6al Arrow G indicates the direction of the force of gravitY
6~5 and Arrow T the direction of the rotation of the cam gear.
Next, Fig.4 shows another embodiment in accordance with the invention in which the like reference numerals are provided for the like parts as those in aforesaid embodiment in Fig.1, thus a further explanation being eliminated. A moving member 28 with an opening 29 resembling the human heart at the center is located on the side of the gear 6 with the opening 29 being so disposed as to surround the camshaft l, and, from a narrow protrusion 29a on the opening 29, the tappet lifting arm.25 extends towards the cam 2 to push up the tapPet 3 in the comPression stroke of the engine. Furthermore, the moving member 28 is suPPorted slidablY
on the side of the gear 6 in the direction aPart from the camshaft 1, bY Pins 32 and 33 Planted on the side of the gear 6 which en8a~e respectivelY in an L-shaped guide slot 30 and an L-shaped cutout guide slot 31 situated at both oPPosite ends of the moving member 28 relating to the camshaft 1 on the line perpendicular to that of the up and down movement of the tappet
The force acting on the moving member against the centrifugal force consis-ts of the force of gravi-ty to the moving member and a Erictional force between -the guide slots and the pins.
In normal sp~eds, th~ c~ntrifugal Eorce on the moviny member induced by the rotation speed of -the engine is so designed to overcome the opposite force acting on the moving member so that the moving member moves to such a position that the fact of the tappet-lifting arm comes down level with or inward of the cam base cirle.
In the accompanying drawings, there are shown illus-trative embodiments of the invention from which these and other of its objectives, novel features and advantages will be readily apparent.
FIG. 1 is a front view of an embodiment for an automatic compression releasing device for the four-cycle engine in accordance with the invention;
FIG. 2 is a sectional view taken along line A-A in Fig. l;
FIG. 3 is a front view of the au-tomatic compression 6~i releasing device in Fig. 1 in the normal operating condition;
FIG. 4 is a front view of another embodiment of an automatic compression releasing device for the four-cycle engine in accordance with the invention;
FIG. 5 is a front view of the automatic compression releasing device in Fig. 4 in the normal operating condition;
FIGS. 6a through 6e are illustrations of the opera-tion of the embodiment shown in Fig. l; and FIG. 7 is a front view showing a typical type of the automatic compression releasing device for the four-cycle engine in accordance with the prlor art.
R~ferring Eirs-tly to Figur~ 7, which lllustra-tes th~ prior art o-E ~apanes~ Utllity Model No. 1~207C0 and enti-tled "Au-toma-tic compression Releasing oE Internal Combus-tion Engine", there is shown a typical example of the automatic compression releasing devices, and relating to the four-cycle engine in which the rotation of the cam shaft 1 causes the intake or exhaust valve 5 in the combustion chamber 4 to be opened or closed by reciprocating the tappet 3 through a combination of the cam 2 on the cam shaft 1 and the valve spring 34. The automatic compression releasing device com-prises an arcuate moving member 7 rotatably supported by a pin ~ approximately at its center on one half of a side face of the gear 6 integrated with the cam shaft 1 having the cam 2 actuating an either valve as described above; an arm 9 projecting sideways from one end of the inner circumference of the moving member 7 to push up the tappet 3; another arcuate moving member 10 ùisposed on the other half of the :i . .
1, _ ~ _ side face of the gear 6; one end of the member 10 rotatably supported by another pin 11 on one end of aforesaid moving member 7; the other end of the moving member 10 provided on its outer circumference with the guide 12 consisting of a plurality of semi-circle recesses to engage with the separa-te pin 1.3 attached on the side face of the gear 6; and a spring 14 extended between one point on said other end of the moving member 10 and the other point on the moving member 7 located on the side opposite to the pin 11 relative to the pin 8.
In the start while -the engine rpm is still low, the moving members 7 and 10 of the automatic compresslon releasing device are held ln place, since the spri.ng 14 is pulling the lower end of the moving member 7 close to the mov:ing member 10 against its then small centrifugal force. Since the arm 9 extended sidewards from the inner circumference of the moving member 7 then takes a position projecting out of the cam base circle 2, the arm 7 pushes up the tappet 3 in the compression stroke for every rotation of -the cam shaf-t 1 to slightly open the valve 5, thus letting out a par-t of compressed gas mixture resulting in a reduction of starting torque.
On the other hand, as the engine rpm comes up, since the moving members 7 and 10 swing outward respectively about the pins 8 and 11 due to their centrifugal forces over-coming the force of the spring 14, aforesaid arm 9 changes the position inwards of the base circle 2a of the cam 2, thus losing the function of pushing up the tappet 3, resulting in the valve 5 being intact in the compression stroke to have the normal closing function of the valve 5 following only the cam 2 on -the cam shaft 1.
6~
Referring now to the drawings depicting in detail embodimen-ts in accordance with the invention, Figs. 1 and 2 illustrate an embodiment of an automatic compression releasing device for the four-cycle engine. In these drawings, 1 is a cam shaft and 2 is a cam fitted on the cam shaft 1. Tappet 3 opens and closes an intake or exhaust valve 5 in a combustion chamber, which is reciprocated by the cam 2 and a valve spring 34. Gear 6 is mounted on the cam shaft 1 next to cam 2, and on the side of said gear 6 a moving member 20 is disposed surrounding about a half of the cam shaft 1. The moving member 20 is slidably supported outwards along the side of gear 6 by pins 23 and 24 planted in the side of gear 6 through an elllptlcal gulde slot 21 and an L-shaped gulde slo-t 22 which are .respect.ively bord sldeways ln the opposi.te slcles ~.n relation to th~ sha:Et c~nt~r.l.:i.n~ of the cam shaft .l. 'rhe movlng member 20 has an arrn 25 projectlng sldewards, ln order to llft the tappet 3 at least ln the compresslon stroke. In thls embodlment, a sprlng 27 ls so extended between the tappet llftlng arm 25 and a hole 26 drllled in the side of -the gear 6 that said tappet lifting arm 25 ls forced to project radlally out of the base clrcle 2a of the cam Z durlng the cranking perlod when the englne ls bei.ng started. The base clrcle 2a of the cam 2 ls partly removed ln order -tha-t the cutout can accommoda-te the protrudlng tappet llftlng arm 25.
In the embodlment of the automatlc compresslon releasing devlce according to the lnventlon as described abover while the engine is at rest, the movlng mernber 20 ls pulled by the sprlng 27 toward the hole 26, and also is helped by the engagement of . ~ - 6 -.. ........ j 6~
the pins 23 and 24 planted in the side of the gear 6 with the guide slots 21 and 22 so that the taPPet lifting arm 25 takes such a position out of the base circle of the cam as to effect the compression releasing function.
~'hen cranking the engine at the start, the moving member 20 receives a small centrifugal force corresPonding to the rotation speed of the cam shaft 1. But at this time, since the centrifugal force never exceeds the resultant force of the gravity to the moving member, a frictional force between the pin 24 and the guide slot ~2, and a tension of the sPring 27, the moYing member 20 has no relative movement to the gear 6, thus resulting in the tappet liftin~ arm 25 Proiecting out of the base circle 2a of the cam 2. Therefore, in the compression stroke, the tappet is raised by the tapPet lifting arm 25 while the moving member 20 being supported by the guide slot 22 and the pin 24, resulting in the Yalve 5 remaining oPen until near the top dead point of compres-sion stroke to allow the gas mixture to escape, thus minimizing the starting torque.
hs the engine reaches the normal operating condition gathe-ring speed, induced by the centrifugal force which has become greater than the resultant f orce of said graYitational f orce, f rictional f orce and pull of the spring 27, the moving member 20 begins to rotate around the pin 23, thus causing the pin 24 opposite to the pin 23 to move to the edge of the bent portion in the guide slot 22. Since from this po int both guide slots 22 and 21 have the same direction as shown in Fig.3, the moving member 20 begins to slide outwards (downwards) along the side of the gear 6. thus causing the tappet lifting arm 25 receding back into the cutout on the camshaft 1 or into the inside of the base circle 2a of the cam 2. resulting in the loss of the function to lift the valve 5. This enables the valve 5 to rcmain closed over 5 the compression stroke in accordance with the normal open-close function of the valve 5 controlled by the cam 2 on the camshaft 1.
When the eng;ne comes to a halt, since the centrifugal force generated on the moving member 20 by the rotation of the engine disaPPears. the moving member 20 is pulled back in place by the pull of the spring 27 as shown in Figs. 1 and 2 to restore the comPreSSion releasing function of the tappet lifting arm 25.
In this embodiment using the spring 27, the moving member 20 is so designed as to be forcibly returned in Place to regain the compression releasing function by the spring 27 when the engine comes to a halt. In the case of the common horizontal engine having the camshaft 1 in the direction perpendicular to that of the gravitational force, however. without the spring 27, the moving member 20 can be returned in place to restore the compres-sion releasing function just before pushing up the tappet 3,through the relative movement of the moving member 20 as shown in Fig.6a throu~h 6e, within the last one rotation of the camshaft 1. when the engine is going to a halt, while losing the centrifu-gal force on the moving member. That's because, in a front view of Fig.1, the gear 6 rotates anticlockwise, and both the slots 21 and 22 are opened diagonally from top right to bottom left. In Fig.6al Arrow G indicates the direction of the force of gravitY
6~5 and Arrow T the direction of the rotation of the cam gear.
Next, Fig.4 shows another embodiment in accordance with the invention in which the like reference numerals are provided for the like parts as those in aforesaid embodiment in Fig.1, thus a further explanation being eliminated. A moving member 28 with an opening 29 resembling the human heart at the center is located on the side of the gear 6 with the opening 29 being so disposed as to surround the camshaft l, and, from a narrow protrusion 29a on the opening 29, the tappet lifting arm.25 extends towards the cam 2 to push up the tapPet 3 in the comPression stroke of the engine. Furthermore, the moving member 28 is suPPorted slidablY
on the side of the gear 6 in the direction aPart from the camshaft 1, bY Pins 32 and 33 Planted on the side of the gear 6 which en8a~e respectivelY in an L-shaped guide slot 30 and an L-shaped cutout guide slot 31 situated at both oPPosite ends of the moving member 28 relating to the camshaft 1 on the line perpendicular to that of the up and down movement of the tappet
3.
With this embodiment of an automatic compression releasing device, when the engine is at rest, the moving member 28 occupies a Position to fulfill the compression releasing function by the help of the PinS 32 and 33 as well as the guide slots 30 and 31.
While the engine is running at a very low sPeed in the initial stage of a start, a centrifugal force in parallel with the rpm of the cam shaft 1 acts on the moving member 28, but this is not large enough to overcome the sum of the frictional resis-tances between the guide slot 30 and the pin 32 as well as :~26~6~
between the guide slot 31 and the pin 33. Therefore. no movement of the moving member 28 relative to the cam gear ô takes place, keeping the tappet lifting arm 25 PrCieCting out of the base circle 2a of the cam 2, resulting in that in the compression stroke the tappet 3 is kePt raised bY being suPPorted through the tappet lifting arm 25 with the guide slot 30 and the pin 32 as well as the guide slot 31 and the Pin 33. Thus, the valve 5 is kePt open until near the top dead Point of comPression stroke letting the compressed gas mixture to escape to lower the inside pressure and minimize the start torque.
Once the engire has reached the steadY oPerating condition after an increase of the engine rPm, since the centrifugal force acting on the moving member surPasses the combined frictional force between the guide slots 30 and 31 and the pins 32 and 33, the moving member 28, as shown in Fig.5, slides outwards of the gear 6 along the pins 32 and 33 engaged in the guide slots 30 and 31, in the direction oblique to that of the reciprocating move-ment of the tapPet 3, thus leading the tapPet lifting arm 25 recedin8 into the cutout in the base circle 2a of the cam 2. This dePriYes the tappet 3 of its lifting function, with the result that the valve 5 is kePt comPletelY closed over the comPression stroke, so that the oPen-close function of the valYe 5 is perfor-med normally, follow;ng the movement of the cam 2 on the cam shaft 1.
This embodiment is apPlied to the horizontal tYPe engine having the cam shaft 1 disPosed in the direction Perpendicular to that of the gravity. In Fig.4, since the force of gravitY acts ~Z6~6~S
downwards and the gear 6 revolves anticlockwise viewing from front, when the engine is nearing a halt with a minimum of the centrifugal force. the moving member 28 returns to the Position where it can regain the comPression releasing function right before pushing the tappet 3 up.
Though, in each of these embodiments, the pins are planted on the gear side and the guide slots opened in the moving mem-bers, the reverse is also possible, in which the guide slots are opened on the gear side and the pins`.are planted on the moving member.
As eYident from the descriPtion given above, because the automatic compression releasing devics for the 4 cYc]e engines according to the invention requires only a single moving member actuated by the centrifugal force due to the revolution of the cam shaft, and the return spring is not necessarily required in the general vertical tYpe engine, the device can be easily moun-ted because of its exceedinglY simple structure.
Since only one moving member serves-to Perform the compres-sion releasing function and the tappet is directly pushed uP
20 without anY additional means between them, the automatic compres-sion releasing device can oPerate in an accurate fashion so as to reduce smooth the start torque and to imProve remarkably the oPerabilitY of the engine in the start.
In addition, an aPPropriate determination of the shape of 25 the moving member and a proPer design of the center of gravity can eliminate the need for the return sPring with the like effect achieved.
With this embodiment of an automatic compression releasing device, when the engine is at rest, the moving member 28 occupies a Position to fulfill the compression releasing function by the help of the PinS 32 and 33 as well as the guide slots 30 and 31.
While the engine is running at a very low sPeed in the initial stage of a start, a centrifugal force in parallel with the rpm of the cam shaft 1 acts on the moving member 28, but this is not large enough to overcome the sum of the frictional resis-tances between the guide slot 30 and the pin 32 as well as :~26~6~
between the guide slot 31 and the pin 33. Therefore. no movement of the moving member 28 relative to the cam gear ô takes place, keeping the tappet lifting arm 25 PrCieCting out of the base circle 2a of the cam 2, resulting in that in the compression stroke the tappet 3 is kePt raised bY being suPPorted through the tappet lifting arm 25 with the guide slot 30 and the pin 32 as well as the guide slot 31 and the Pin 33. Thus, the valve 5 is kePt open until near the top dead Point of comPression stroke letting the compressed gas mixture to escape to lower the inside pressure and minimize the start torque.
Once the engire has reached the steadY oPerating condition after an increase of the engine rPm, since the centrifugal force acting on the moving member surPasses the combined frictional force between the guide slots 30 and 31 and the pins 32 and 33, the moving member 28, as shown in Fig.5, slides outwards of the gear 6 along the pins 32 and 33 engaged in the guide slots 30 and 31, in the direction oblique to that of the reciprocating move-ment of the tapPet 3, thus leading the tapPet lifting arm 25 recedin8 into the cutout in the base circle 2a of the cam 2. This dePriYes the tappet 3 of its lifting function, with the result that the valve 5 is kePt comPletelY closed over the comPression stroke, so that the oPen-close function of the valYe 5 is perfor-med normally, follow;ng the movement of the cam 2 on the cam shaft 1.
This embodiment is apPlied to the horizontal tYPe engine having the cam shaft 1 disPosed in the direction Perpendicular to that of the gravity. In Fig.4, since the force of gravitY acts ~Z6~6~S
downwards and the gear 6 revolves anticlockwise viewing from front, when the engine is nearing a halt with a minimum of the centrifugal force. the moving member 28 returns to the Position where it can regain the comPression releasing function right before pushing the tappet 3 up.
Though, in each of these embodiments, the pins are planted on the gear side and the guide slots opened in the moving mem-bers, the reverse is also possible, in which the guide slots are opened on the gear side and the pins`.are planted on the moving member.
As eYident from the descriPtion given above, because the automatic compression releasing devics for the 4 cYc]e engines according to the invention requires only a single moving member actuated by the centrifugal force due to the revolution of the cam shaft, and the return spring is not necessarily required in the general vertical tYpe engine, the device can be easily moun-ted because of its exceedinglY simple structure.
Since only one moving member serves-to Perform the compres-sion releasing function and the tappet is directly pushed uP
20 without anY additional means between them, the automatic compres-sion releasing device can oPerate in an accurate fashion so as to reduce smooth the start torque and to imProve remarkably the oPerabilitY of the engine in the start.
In addition, an aPPropriate determination of the shape of 25 the moving member and a proPer design of the center of gravity can eliminate the need for the return sPring with the like effect achieved.
Claims (2)
1. An automatic compression releasing device for reducing the gas pressure in a combustion chamber of a four-cycle engine for use in starting the four-cycle engine in which intake and exhaust valves are opened and closed by reciprocating tappets by means of the rotation of a cam on a cam shaft through its rotation, comprising:
a single moving member being disposed on a side of a gear integrated with the cam shaft in such a way as to surround said cam shaft;
a tappet-lifting arm being extended from said moving member to a position where it can push up a tappet in a compression stroke of the engine;
two guide slots being bored in said moving member, and two pins being planted in said gear, so as to engage with said respective slots, where the engagement of said pins with said slots allows said moving member to slide independently along with the side of said gear in a predeter-mined direction; and in the cranking stage, a centrifugal force acting on said moving member in parallel with the rotation speed being designed not to overcome a force acting on said moving member against the centrifugal force, resulting in said moving member being so retained at a position that a face of said tappet-lifting arm being kept as projecting outside a base circle of the cam, and a returning force of said moving member acting on said tappet-lifting arm through said tappet being able to be sustained by the combination of said slots and said pins;
said force acting on said moving member against the centrifugal force consisting of the force of gravity to said moving member and a frictional force between said guide slots and said pins; and in normal speeds, the centrifugal force on said moving member induced by the rotation speed of the engine being so designed to overcome the opposite force acting on said moving member so that said moving member moves to such a position that the face of said tappet-lifting arm comes down level with or inward of said cam base circle.
a single moving member being disposed on a side of a gear integrated with the cam shaft in such a way as to surround said cam shaft;
a tappet-lifting arm being extended from said moving member to a position where it can push up a tappet in a compression stroke of the engine;
two guide slots being bored in said moving member, and two pins being planted in said gear, so as to engage with said respective slots, where the engagement of said pins with said slots allows said moving member to slide independently along with the side of said gear in a predeter-mined direction; and in the cranking stage, a centrifugal force acting on said moving member in parallel with the rotation speed being designed not to overcome a force acting on said moving member against the centrifugal force, resulting in said moving member being so retained at a position that a face of said tappet-lifting arm being kept as projecting outside a base circle of the cam, and a returning force of said moving member acting on said tappet-lifting arm through said tappet being able to be sustained by the combination of said slots and said pins;
said force acting on said moving member against the centrifugal force consisting of the force of gravity to said moving member and a frictional force between said guide slots and said pins; and in normal speeds, the centrifugal force on said moving member induced by the rotation speed of the engine being so designed to overcome the opposite force acting on said moving member so that said moving member moves to such a position that the face of said tappet-lifting arm comes down level with or inward of said cam base circle.
2. An automatic compression releasing device as claimed in claim 1, wherein the force acting on said moving member against said centrifugal force further including a tension force of a spring extended between said moving member and said gear.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000498400A CA1261695A (en) | 1985-12-20 | 1985-12-20 | Automatic compression releasing device for four-cycle engine |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000498400A CA1261695A (en) | 1985-12-20 | 1985-12-20 | Automatic compression releasing device for four-cycle engine |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1261695A true CA1261695A (en) | 1989-09-26 |
Family
ID=4132151
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000498400A Expired CA1261695A (en) | 1985-12-20 | 1985-12-20 | Automatic compression releasing device for four-cycle engine |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1261695A (en) |
-
1985
- 1985-12-20 CA CA000498400A patent/CA1261695A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry |