CN203347874U - Gasoline engine - Google Patents

Abstract

The utility model discloses a gasoline engine which comprises a box body, a box cover, an air cylinder cover, a magneto ignition device, a crankshaft and connecting rod mechanism, a starting device, a fan cover, a speed adjusting device, an air distributing device and a corresponding feeding device. A combustible mixture of fuel oil and air is provided through the feeding device, and the speed adjusting device controls the feed amount of the combustible mixture. The gasoline engine is characterized in that the air distributing device comprises an exhaust valve, an inlet valve and a cam shaft pressure reducing device. At the starting preliminary stage of the gasoline engine, due to the function of a torsional spring, the inlet valve is abutted for exhaust through the right end of an ejector rod, and when the rotating speed of the cam shaft is improved to 500RPM, under the action of centrifugal force, a centrifugal block overcomes twisting force of the torsional spring and rotates backwards with a hinge pin as the rotating axis. A free end of the centrifugal block is prevented from touching a driven gear through a limit pin of a limit device, meanwhile the centrifugal block recedes by a section of distance to enable the ejector rod to move leftwards, the right end of the ejector rod is retracted in a base circle of an inlet cam, venting decompression is stopped, and normal work of the gasoline engine is ensured.

Description

A kind of petrol engine

Technical field

The utility model relates to field of internal combustion engine, is specifically related to a kind of petrol engine.

Background technique

Internal-combustion engine is that fuel (gasoline, diesel oil, coal gas etc.) the produced heat energy that burns in its firing chamber is converted into to a kind of dynamic power machine of mechanical energy.Petrol engine is a kind of as internal-combustion engine, because its simple structure, light and handy, low cost, work balance, noise are also little, be widely used on the truck of motorcycle, car and little carrying capacity, and as requiring compact internal combustion engine lightweight, easy to carry in industrial and agricultural production and national defense construction.

Internal-combustion engine can not start voluntarily, make petrol engine proceed to working state by state of rest, must first by external force, drive the crankshaft rotating of petrol engine, make piston reciprocates, so that after being compressed to a certain degree by inflammable mixture, refire burning, the high temperature and high pressure gas after burning promotes piston and makes crankshaft rotating, and petrol engine could turn round voluntarily.Petrol engine is transitioned into the process of running voluntarily by external force by state of rest, is called gasoline starting.Complete the required device of starting process, be called starting arrangement, starting arrangement comprises Power Drive Unit and starting aid.Power Drive Unit is for overcoming the starting resistance of petrol engine, and starting aid is in order to make gasoline starting light, rapid and reliable.Common are starting drive and as what the internal-combustion engine of hand (drawing) starting was provided with the starting of starting dog and motor actuating motor etc., the employing portable type hand-pulling recoil Starting mode also had be housed.The petrol engine that pulls rope starter all adopts magneto ignition equipment, and starting speed is higher.Therefore, tow too hard during starting, make petrol engine in the instantaneous starting speed that reaches, the gasoline starting success.

After petrol engine cuts out, piston of gasoline engine can stop, and is because piston two ends stress balance.After petrol engine is flame-out, due to inertia, the crank-connecting rod piston mechanism also will be proceeded to pump.The cylinder end valve normal switch, when in compression stroke, due to valve, in closed condition, the cylinder internal air pressure can not reduce pressure voluntarily.The position cylinder internal air pressure that now piston stops is relatively high, when gasoline engine starting moment, need air amount to be compressed, near the compression terminal, can produce very large resistance to compression pression, directly start if the cylinder internal air pressure is not carried out to pressure release, start the initial stage resistance larger, start-up course is difficulty relatively, and especially to discharge capacity, large petrol engine is all the more so.In order to make gasoline engine starting more smooth, generally adopt the device that cylinder pressure while reducing gasoline engine starting is set on protruding axis for gasoline machine, to guarantee the smooth startup of petrol engine.

Chinese patent literature CN200961495Y(number of patent application 200620111527.2) a kind of " camshaft decompression mechanism of motor " disclosed, wherein put down in writing: " Fig. 3, Fig. 4 are in running order for this mechanism of decompressor, and its driven gear is made with nylon material.After engine start, along with the raising of camshaft rotational speed, the torsion generation centrifugal motion that centrifuge arm overcomes torsion spring rotates to a side, until spacing limited part contacts with camshaft for centrifugal motion, is restricted no longer displacement."; this structure contacts and carries out spacing to centrifuge arm with camshaft by the limited part spacing for centrifugal motion; while working due to camshaft in the High Rotation Speed state; therefore for centrifugal motion, spacing limited part easily causes the wearing and tearing to camshaft; secondly can produce a large amount of heats, have serious potential safety hazard.

The model utility content

The purpose of this utility model is to provide a kind of simple in structure, the safe and reliable petrol engine with Cam shaft pressure reducing device.

The basic technical scheme of realizing the utility model purpose is: a kind of petrol engine, comprise casing, case lid, cylinder head, magneto ignition equipment, connecting rod, starting drive, fan housing, arrangements for speed regulation, air distributing device and corresponding supplier, the inflammable mixture of fuel oil and air is provided by supplier.Arrangements for speed regulation are controlled the input of inflammable mixture.Be provided with cylinder in casing, cylinder is for guiding the cylindrical space of piston reciprocates.Be provided with cylinder liner in cylinder.Case lid is airtight to be fixedly installed on the rear side lower part of casing.Cylinder head is airtight to be fixedly connected on the top of casing, and is provided with head gasket between the contacted part of cylinder head and casing.Magneto ignition equipment is fixed on by its spark coil on the front side of casing, and the spark plug of magneto ignition equipment screws and is fixed on cylinder head.Connecting rod comprises piston, connecting rod, bent axle, timing gear and flywheel.Piston is slidably matched and is arranged in the cylinder liner of casing, and bent axle is arranged on casing and case lid to horizontally rotating along left and right by its axis.Connecting rod has its upper and lower two ends to be rotationally connected with piston and bent axle respectively.Timing gear are arranged on bent axle, and are positioned at the right side of connecting rod.Flywheel is fixedly installed on bent axle and is positioned at the casing left side.Corresponding space between cylinder head and casing and piston forms the bags of petrol engine.Starting drive is the hand-pulling recoil starting drive, and starting drive comprises handle tray and starts the pawl dish.Start the pawl dish and coaxially be fixedly connected with bent axle, and be positioned on the left end of bent axle.Starting the pawl dish coordinates and is connected with the mutual clamping of flywheel.Fan housing is fixed on casing, and from left, the appropriate section of flywheel and startup pawl dish is covered.Handle tray is fixed on the left side of fan housing.Its structural feature is: air distributing device comprises exhaust valve, intake valve and Cam shaft pressure reducing device.Exhaust valve and intake valve are slidably matched and are arranged on casing respectively.Cam shaft pressure reducing device comprises camshaft, driven gear, centrifugal-block, limit stoper, resetting means and push rod.Camshaft is provided with exhaust cam and intake cam from top to down successively.Driven gear is fixed on camshaft by corresponding key, and is positioned at the intake cam below.Camshaft is provided with the jogger hole that runs through its left and right through its axis.Jogger hole is between intake cam and driven gear, and the angle α of the axis of jogger hole and camshaft is 60 to 80 degree.The intake cam lower right side is provided with the push rod breach.Centrifugal-block is the steel integral piece, and integral body is the semicircle annular.The right-hand member fixed point end of centrifugal-block is arranged on the upside of driven gear by corresponding bearing pin or screw turns, and around the camshaft setting.The left end free end of centrifugal-block is provided with push pedal.Push pedal is high outside and low outside setting, and push pedal is identical with angle α with the angle of horizontal plane.The intersection of push pedal and horizontal plane is 19 degree to 25 degree with the axis through camshaft along front and back to the angle β of the vertical guide arranged.The left end free end of centrifugal-block also is provided with along front and back to the oval shape restraining groove arranged.Limit stoper is position limit pin or screw, and position limit pin is arranged on driven gear through vertical after the restraining groove of centrifugal-block by its underpart, for limiting the free-ended displacement of centrifugal-block.Resetting means is arranged between driven gear and centrifugal-block, for resetting of centrifugal-block.Push rod is slidably matched and is arranged in the jogger hole of camshaft, and its lower end contacts with the push pedal of centrifugal-block, and the right-hand member head corresponding site of push rod is arranged in the push rod breach.

The above-mentioned basic technical scheme of take as basic technological scheme is: the driven gear of described Cam shaft pressure reducing device is provided with mounting hole, the blind hole that mounting hole is opening upwards.The right part of centrifugal-block is provided with buckling groove.Resetting means is torsion spring, and an end of torsion spring is fixedly installed in the mounting hole of driven gear, and the other end is fixedly installed in the buckling groove of centrifugal-block.

The technique scheme of take as basic technological scheme is: the push rod of Cam shaft pressure reducing device is multidiameter shaft shape left large and right small, and the right-hand member head of push rod is hemisphere face.The left end of push rod is between the push pedal of camshaft and centrifugal-block, and the left side corresponding site of push rod contacts in the corresponding site of push pedal.The right-hand member of push rod stretches out outside camshaft to the right.

Above-mentioned each appropriate technical solution of take as basic technological scheme is: the camshaft of described Cam shaft pressure reducing device is integrated part.

The technique scheme of take as basic technological scheme is: the periphery of the centrifugal-block of Cam shaft pressure reducing device is provided with Weight plate, and Weight plate is along circumferentially vertically being arranged on the rear side periphery of centrifugal-block.

The technique scheme of take as basic technological scheme is: the middle part downside of the centrifugal-block of Cam shaft pressure reducing device is provided with slide protrusion.

The utlity model has positive effect: (1) petrol engine of the present utility model is simple in structure, and easily, cost is lower in assembling, and when petrol engine is worked, camshaft is in the High Rotation Speed state, and with centrifugal-block, do not contact, and safety reliability is high.(2) the left end free end of centrifugal-block of the present utility model is provided with push pedal; Push pedal is high outside and low outside setting, and the angle α of the angle of push pedal and horizontal plane and the axis of jogger hole and camshaft is identical, can be effectively by active force effect and push rod.(3) axis of the intersection of the push pedal of centrifugal-block of the present utility model and horizontal plane and process camshaft is along front and back to the vertical guide setting at an angle arranged, can guarantee centrifugal-block under centrifugal action when overcoming the active force of resetting means torsion spring, its free end just can guarantee that in the right-hand member head indentation intake cam basic circle of push rod, intake valve is return fully in the very little scope of moving.(4) centrifugal-block of the present utility model is provided with Weight plate, be conducive to centrifugal-block under centrifugal action at the active force that overcomes the resetting means torsion spring, make the gasoline function enter fast normal working.(5) the middle part downside of centrifugal-block of the present utility model is provided with slide protrusion, greatly reduced the area of contact of centrifugal-block and driven gear, be conducive to that centrifugal-block is overcoming the active force motion of resetting means torsion spring under centrifugal action or Rapid reset under the active force of resetting means torsion spring.(6) resetting means of the present utility model adopts torsion spring, simple in structure, easy for installation, uses reliable.(7) push rod of the present utility model adopts multidiameter shaft shape structure left large and right small, easy for installation, and can prevent that it from coming off from jogger hole while installing.(8) adopt the petrol engine of Cam shaft pressure reducing device of the present utility model in initial start stage, effect due to torsion spring, the right-hand member crown of push rod the intake valve exhaust, along with camshaft speed improves, arrive the 500RPM left and right, under centrifugal action, centrifugal-block will overcome the torsion of torsion spring, and the bearing pin of take rotates backward as rotatingshaft; By preventing that by the limit stoper position limit pin free end of centrifugal-block from encountering driven gear, abdicate a segment distance can be to left movement by push rod simultaneously, the time push rod the basic circle of right-hand member head indentation intake cam in, stop the decompression of losing heart, guarantee the petrol engine normal operation.

The accompanying drawing explanation

Structural representation when Fig. 1 is petrol engine case lid open mode of the present utility model, wherein case lid does not draw.

Schematic diagram when Fig. 2 is the right-hand observation of Fig. 1.

The structural representation that Fig. 3 is petrol engine while observing from the left of Fig. 1, wherein spark plug does not draw.

Fig. 4 is that cross-sectional schematic is amplified at the I place in Fig. 3.

The schematic diagram that Fig. 5 is the Cam shaft pressure reducing device in Fig. 1.

Fig. 6 is the A-A sectional view in Fig. 5, and wherein centrifugal-block, resetting means and push rod do not draw.

The left view that Fig. 7 is Fig. 5, wherein intake valve does not draw.

Fig. 8 is the schematic diagram after Fig. 7 removes camshaft.

The schematic diagram that Fig. 9 is the camshaft in Fig. 5.

The schematic diagram that Figure 10 is the centrifugal-block in Fig. 7.

Mark in above-mentioned accompanying drawing is as follows:

Casing 100, cylinder 101, cylinder liner 102, radiating fin 103, cylinder head 200, cylinder head fin 201, magneto ignition equipment 300, spark coil 301, spark plug 302, connecting rod 400, piston 401, connecting rod 402, bent axle 403, timing gear 404, flywheel 405, starting drive 500, handle tray 501, start pawl dish 502, fan housing 600, arrangements for speed regulation 700, speed regulation gear 701, air distributing device 900, intake valve 901

Camshaft 1, exhaust cam 11, intake cam 12, push rod breach 12-1, jogger hole 13, driven gear 2, mounting hole 21, centrifugal-block 3, push pedal 31, restraining groove 32, buckling groove 33, Weight plate 34, slide protrusion 35, limit stoper 4, resetting means 5, push rod 6.

Embodiment

The description in orientation of the present utility model is carried out according to the orientation shown in Fig. 1, is also the direction up and down that the direction up and down shown in Fig. 1 is description, and a side of court of Fig. 1 institute is the place ahead, and a side who deviates from Fig. 1 is rear.

(embodiment 1)

See Fig. 1 to Fig. 3, petrol engine of the present utility model comprises casing 100, case lid, cylinder head 200, magneto ignition equipment 300, connecting rod 400, starting drive 500, fan housing 600, arrangements for speed regulation 700 and air distributing device 900.Petrol engine of the present utility model also is furnished with corresponding supplier, and the inflammable mixture of fuel oil and air is provided by supplier.Control the input of inflammable mixture by arrangements for speed regulation 700, thereby regulate the rotating speed of petrol engine.

See Fig. 1 to Fig. 3, casing 100 is aluminium die cast integral piece.Be provided with cylinder 101 in casing 100, cylinder 101 is for being used for guiding the cylindrical space of piston reciprocates.Be provided with cylinder liner 102 in cylinder 101.Case lid is airtight to be fixedly installed on the rear side lower part of casing 100.Also be provided with the radiating fin 103 for dispelling the heat accordingly on casing 100.Cylinder head 200 is airtight to be fixedly connected on the top of casing 100, and is provided with head gasket between the contacted part of cylinder head 200 and casing 100.Cylinder head 200 is provided with cylinder head fin 201.Magneto ignition equipment 300 is fixed on the front side of casing 100 by its spark coil 301, and the spark plug 302 of magneto ignition equipment 300 screws and is fixed on cylinder head 200.

See Fig. 1 to Fig. 3, connecting rod 400 comprises piston 401, connecting rod 402, bent axle 403, timing gear 404 and flywheel 405.Piston 401 is slidably matched in the cylinder liner 102 that is arranged on casing 100, and bent axle 403 is arranged on casing 100 and case lid to horizontally rotating along left and right by its axis.Connecting rod 402 has its upper and lower two ends to be rotationally connected with piston 401 and bent axle 403 respectively.Timing gear 404 are arranged on bent axle 403, and are positioned at the right side of connecting rod 402.Flywheel 405 is fixedly installed on bent axle 403 and is positioned at casing 100 left sides.Corresponding space between cylinder head 200 and casing 100 and piston 401 forms the bags of petrol engine.

See Fig. 1, starting drive 500 is the hand-pulling recoil starting drive, and starting drive 500 comprises handle tray 501 and starts pawl dish 502.Start pawl dish 502 and coaxially be fixedly connected with bent axle 403, and be positioned on the left end of bent axle 403.Starting pawl dish 502 coordinates and is connected with the mutual clamping of flywheel 405.Fan housing 600 is fixed on casing 100, and from left, the appropriate section of flywheel 405 and startup pawl dish 502 is covered.Handle tray 501 is fixed on the left side of fan housing 600, drive and start 502 rotations of pawl dish by handle tray 501, and then 403 rotations of band dynamic crankshaft starts petrol engine.

See Fig. 1 to Fig. 4, air distributing device 900 comprises exhaust valve, intake valve 901 and Cam shaft pressure reducing device.Exhaust valve and intake valve 901 are slidably matched respectively and are arranged on casing 100.

See Fig. 4, Fig. 5, Fig. 7 and Fig. 8, Cam shaft pressure reducing device comprises camshaft 1, driven gear 2, centrifugal-block 3, limit stoper 4, resetting means 5 and push rod 6.

See Fig. 5 to Fig. 9, camshaft 1 is the steel integral piece.Camshaft 1 is provided with exhaust cam 11 and intake cam 12 from left to right successively.Intake cam 12 right upper portion are provided with push rod breach 12-1.Driven gear 2 is fixed on camshaft 1 by corresponding key, and it is right-hand to be positioned at intake cam 12.Camshaft 1 is provided with its upper and lower jogger hole 13 that runs through through its axis.Jogger hole 13 is between intake cam 12 and driven gear 2, and jogger hole 13 is 60 to 80 degree (the present embodiment is 75 degree) with the angle α of the axis of camshaft 1.Driven gear 2 is provided with mounting hole 21, and mounting hole 21 is opening blind hole left.Camshaft 1 is arranged on casing 100 and case lid to horizontally rotating along left and right.Driven gear 2 is meshed with the timing gear 404 of connecting rod 400.Arrangements for speed regulation 700 are fixedly installed on case lid, are positioned at the place, lower right of casing 100, and the speed regulation gear 701 of arrangements for speed regulation 700 is meshed with driven gear 2.See Fig. 4, Fig. 6, Fig. 7 and Fig. 9, centrifugal-block 3 is the steel integral piece, and integral body is semi-circular.The upper end fixed point end of centrifugal-block 3 rotates and is arranged on the left side of driven gear 2 by corresponding bearing pin 8 or screw (the present embodiment is bearing pin), and arranges around camshaft 1.The center of circle of centrifugal-block 3 is positioned on the axis of camshaft 1.The top of centrifugal-block 3 is provided with buckling groove 33.The lower end free end of centrifugal-block 3 is provided with push pedal 31.Push pedal 31 is high outside and low outside setting, and push pedal 31 is identical with angle α with the angle of vertical guide.Push pedal 31 is 19 degree to 25 degree (the present embodiment are 19 degree) with the axis through camshaft 1 along front and back to the angle β of the horizontal plane arranged with the intersection of vertical guide.The lower end free end of centrifugal-block 3 also is provided with along front and back to the oval shape restraining groove 32 arranged.The periphery of centrifugal-block 3 is provided with Weight plate 34, and Weight plate 34 is along circumferentially vertically being arranged on the rear side periphery of centrifugal-block 3.The middle part downside of centrifugal-block 3 is provided with slide protrusion 35, and slide protrusion 35 is that downward punching press forms from the top of centrifugal-block 3.

See Fig. 7 and Fig. 8, limit stoper 4 is position limit pin or screw (the present embodiment is position limit pin), and by its underpart, the rear vertical of restraining groove 32 through centrifugal-block 3 is arranged on driven gear 2 position limit pin, for limiting the free-ended displacement of centrifugal-block 3.

See Fig. 7 and Fig. 8, resetting means 5 is torsion spring, and an end of torsion spring is fixedly installed in the mounting hole 21 of driven gear 2, and the other end is fixedly installed in the buckling groove 33 of centrifugal-block 3.

See Fig. 4 and Figure 10, push rod 6 is multidiameter shaft shape left large and right small, and the right-hand member head of push rod 6 is hemisphere face.Push rod 6 inserts in the jogger hole 13 of camshaft 1 from bottom to up, and can slide up and down.The diameter of the end portion of push rod 6 is greater than 1 millimeter to 3 millimeters, the aperture (the present embodiment is 2 millimeters) of the jogger hole 13 of camshaft 1.The upper tip corresponding site of push rod 6 is arranged in push rod breach 12-1.The lower end of push rod 6 is between the push pedal 31 of camshaft 1 and centrifugal-block 3, and the lower end surface corresponding site of push rod 6 contacts in the corresponding site of push pedal 31.The upper end of push rod 6 protrudes upward outside camshaft 1.

Cam shaft pressure reducing device of the present utility model is applied in corresponding petrol engine while using, before gasoline engine starting, by resetting means 5(, be also torsion spring) active force, make the lower end free end of centrifugal-block 3 near camshaft 1, thereby push push rod 6 to top by push pedal 31, now the upper tip of push rod 6 stretches out intake cam 12 basic circles and withstands intake valve 901 outward, makes intake valve 901 return fully, thereby makes intake valve decompression state in opening when the petrol engine state of rest.

After gasoline engine starting, camshaft 1 and driven gear 2 fast rotational, when reaching certain rotating speed, the active force that centrifugal-block 3 overcomes resetting means 5 be take bearing pin 8 as the rotatingshaft motion under the effect of centrifugal force, its lower end free end is away from camshaft 1, and, by the free-ended move distance of limit stoper 4 restriction centrifugal-blocks 3, the thrust of the push pedal 31 of the suffered centrifugal-block 3 of push rod 6 disappears, intake valve 901 is return fully, and gasoline engine starting is to normal working.

When the petrol engine stall or petrol engine rotational speed while reducing gradually, the suffered centrifugal force of centrifugal-block 3 reduces.Under the effect of the active force of resetting means 5, when the rotating speed of camshaft 1 drops to a certain degree, centrifugal-block 3 resets, the lower end that the free-ended push pedal 31 of centrifugal-block 3 is pushing away push rod 6 moves upward push rod 6, make the upper tip of push rod 6 stretch out the outer position of intake cam 12 basic circles, make intake valve 901 in open mode, discharge gas in the jar, reduce air compressing than the purpose that reaches the decompression state of being convenient to startup.

Above embodiment is only for illustration of the utility model; but not to restriction of the present utility model; person skilled in the relevant technique is not in the situation that break away from spirit and scope of the present utility model; can also make various conversion and variation; in concrete application process, can also transform accordingly according to the inspiration of above-described embodiment, within therefore all technological schemes that are equal to all should be included into scope of patent protection of the present utility model.

Claims (6)

1. a petrol engine, comprise casing (100), case lid, cylinder head (200), magneto ignition equipment (300), connecting rod (400), starting drive (500), fan housing (600), arrangements for speed regulation (700), air distributing device (900) and corresponding supplier, the inflammable mixture of fuel oil and air is provided by supplier; Arrangements for speed regulation (700) are controlled the input of inflammable mixture; Be provided with cylinder (101) in casing (100), cylinder (101) is for being used for guiding the cylindrical space of piston reciprocates; Be provided with cylinder liner (102) in cylinder (101); Case lid is airtight to be fixedly installed on the rear side lower part of casing (100); Cylinder head (200) is airtight to be fixedly connected on the top of casing (100), and is provided with head gasket between the contacted part of cylinder head (200) and casing (100); Magneto ignition equipment (300) is fixed on the front side of casing (100) by its spark coil (301), and the spark plug (302) of magneto ignition equipment (300) screws and is fixed on cylinder head (200); Connecting rod (400) comprises piston (401), connecting rod (402), bent axle (403), timing gear (404) and flywheel (405); Piston (401) is slidably matched in the cylinder liner (102) that is arranged on casing (100), and bent axle (403) is arranged on casing (100) and case lid to horizontally rotating along left and right by its axis; Connecting rod (402) has its upper and lower two ends to be rotationally connected with piston (401) and bent axle (403) respectively; It is upper that timing gear (404) are arranged on bent axle (403), and be positioned at the right side of connecting rod (402); Flywheel (405) is fixedly installed on bent axle (403) above and is positioned at casing (100) left side; Corresponding space between cylinder head (200) and casing (100) and piston (401) forms the bags of petrol engine; Starting drive (500) is the hand-pulling recoil starting drive, and starting drive (500) comprises handle tray (501) and starts pawl dish (502); Start pawl dish (502) and coaxially be fixedly connected with bent axle (403), and be positioned on the left end of bent axle (403); Starting pawl dish (502) coordinates and is connected with the mutual clamping of flywheel (405); It is upper that fan housing (600) is fixed on casing (100), and from left, the appropriate section of flywheel (405) and startup pawl dish (502) is covered; Handle tray (501) is fixed on the left side of fan housing (600); It is characterized in that: air distributing device (900) comprises exhaust valve, intake valve (901) and Cam shaft pressure reducing device; Exhaust valve and intake valve (901) are slidably matched respectively and are arranged on casing (100); Cam shaft pressure reducing device comprises camshaft (1), driven gear (2), centrifugal-block (3), limit stoper (4), resetting means (5) and push rod (6); Camshaft (1) is provided with exhaust cam (11) and intake cam (12) from top to down successively; It is upper that driven gear (2) is fixed on camshaft (1) by corresponding key, and be positioned at intake cam (12) below; Camshaft (1) is provided with the jogger hole (13) that runs through its left and right through its axis; Jogger hole (13) is positioned between intake cam (12) and driven gear (2), and jogger hole (13) is 60 to 80 degree with the angle α of the axis of camshaft (1); Intake cam (12) lower right side is provided with push rod breach (12-1); Centrifugal-block (3) is the steel integral piece, and integral body is the semicircle annular; The right-hand member fixed point end of centrifugal-block (3) is arranged on the upside of driven gear (2) by corresponding bearing pin (8) or screw turns, and arranges around camshaft (1); The left end free end of centrifugal-block (3) is provided with push pedal (31); Push pedal (31) is high outside and low outside setting, and push pedal (31) is identical with angle α with the angle of horizontal plane; Push pedal (31) is 19 degree to 25 degree with the axis through camshaft (1) along front and back to the angle β of the vertical guide arranged with the intersection of horizontal plane; The left end free end of centrifugal-block (3) also is provided with along front and back to the oval shape restraining groove (32) arranged; Limit stoper (4) is position limit pin or screw, and it is upper that position limit pin is arranged on driven gear (2) by its underpart through the rear vertical of the restraining groove (32) of centrifugal-block (3), for limiting the free-ended displacement of centrifugal-block (3); Resetting means (5) is arranged between driven gear (2) and centrifugal-block (3), for resetting of centrifugal-block (3); Push rod (6) is slidably matched in the jogger hole (13) that is arranged on camshaft (1), and its lower end contacts with the push pedal (31) of centrifugal-block (3), and the right-hand member head corresponding site of push rod (6) is arranged in push rod breach (12-1).

2. petrol engine according to claim 1, it is characterized in that: the driven gear of described Cam shaft pressure reducing device (2) is provided with mounting hole (21), the blind hole that mounting hole (21) is opening upwards; The right part of centrifugal-block (3) is provided with buckling groove (33); Resetting means (5) is torsion spring, and an end of torsion spring is fixedly installed in the mounting hole (21) of driven gear (2), and the other end is fixedly installed in the buckling groove (33) of centrifugal-block (3).

3. petrol engine according to claim 2, it is characterized in that: the push rod of Cam shaft pressure reducing device (6) is multidiameter shaft shape left large and right small, and the right-hand member head of push rod (6) is hemisphere face; The left end of push rod (6) is positioned between the push pedal (31) of camshaft (1) and centrifugal-block (3), and the left side corresponding site of push rod (6) contacts in the corresponding site of push pedal (31); The right-hand member of push rod (6) stretches out to the right outside camshaft (1).

4. according to the described petrol engine of one of claims 1 to 3, it is characterized in that: the camshaft of described Cam shaft pressure reducing device (1) is integrated part.

5. petrol engine according to claim 4, it is characterized in that: the periphery of the centrifugal-block of Cam shaft pressure reducing device (3) is provided with Weight plate (34), and Weight plate (34) is along circumferentially vertically being arranged on the rear side periphery of centrifugal-block (3).

6. petrol engine according to claim 5, it is characterized in that: the middle part downside of the centrifugal-block of Cam shaft pressure reducing device (3) is provided with slide protrusion (35).

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