AU2006201016A1 - Air bleeding structure for water-cooled internal combustion engine - Google Patents

Description

S&F Ref: 755622

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address of Applicant Actual Inventor(s): Address for Service: Invention Title: Honda Motor Co., Ltd., of 1-1, Minami-Aoyama 2-chome, Minato-ku, Tokyo, 107-8556, Japan Katsuya Abe Yoshihiko Kumagai Spruson Ferguson St Martins Tower Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) Air bleeding structure for water-cooled internal combustion engine The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845c Air Bleeding Structure for Water-cooled Internal Combustion Engine Field of the Invention The present invention relates generally to an air bleeding structure for a water-cooled internal combustion engine. More specifically, the invention relates to a structure for bleeding air in the pump chamber of a water pump connected to a camshaft provided in a cylinder head as well as for bleeding air in a thermostat valve housing.

Background of the Invention A known example of an air bleeding structure for a water-cooled internal combustion engine is a structure in which a draft is provided at the interior upper portion of a case for housing a thermostat so as to incline upward toward an end face of the case and is used as an air bleeding slope and means is provided for bleeding air from this air bleeding slope to an injection hole side. Such an air bleeding structure is disclosed, for example, in is Japanese Utility Model Laid-open No. Sho 61-182481 (Page 1, Fig. 2).

Meanwhile, in a vehicle having a radiator mounted on the front part of the vehicle body and an engine mounted on the rear part, the engine may be configured such that a housing of a water pump provided outside a cylinder head is provided integrally with a thermostat housing. In this case, respective cooling water passages of the radiator and the engine are connected through a pipe running below an occupant space provided therebetween.

When water is poured into the radiator, therefore, it is necessary to bleed air from both the radiator side and the cooling water passage side of the engine.

If the invention disclosed in Japanese Utility Model Laid-open No. Sho 61-182481 is applied to the vehicle mentioned above, however, the air in the housing for the thermostat [R:MLIBLL] I 8250.doc:J PH can be bled, whereas the air in the pump chamber of the water pump cannot be bled.

Therefore, a passage, a joint and other components should be additionally provided for bleeding the air in the housing for the water pump. This makes it possible to complicate the internal structure of the engine and increase manufacturing cost. If the engine is started up with air remaining in the cooling water passage of the engine, cavitation will occur within the pump chamber, or the air in a water jacket will degrade the cooling performance of the engine.

Objects of the Invention It is the object of the invention to overcome, or at least ameliorate, one or more of the abovementioned disadvantages of the prior art.

It is an object of the invention, at least in its preferred form, to provide an air bleeding structure for a water-cooled internal combustion engine which can collectively bleed the air in the pump chamber of a water pump and that in a housing for a thermostat valve, with simple structure, and which can reduce manufacturing costs.

Summary of the Invention Accordingly, the invention provides an air bleeding structure for a water-cooled internal combustion engine in which a water pump is attached integrally to one end of a camshaft provided in a cylinder head and a thermostat valve housing with a bypass passage is joined integrally to a housing for the water pump, wherein the air bleeding structure is provided with an air bleeding hole which intersects the bypass passage and allows the bypass passage to communicate with a pump chamber of the water pump.

[R:YLIBLL] I 8250.doc:JPH -3- By providing an air bleeding hole that intersects the bypass passage and causes the bypass passage to communicate with the pump chamber of the water pump, air in the pump chamber of the water pump and in the housing for the thermostat valve can be bled in a collective manner. Thus, it is not necessary to additionally provide a passage, a joint and the like used to bleed air, for the housing for the water pump. This allows the internal combustion engine to have a simple configuration, and reduces the number of man-hour for machining and the like and the number of components, thereby providing reduced manufacturing costs.

Preferably, the air bleeding hole includes a first air bleeding hole communicating with the bypass passage and a second air bleeding hole allowing the first air bleeding hole to communicate with the pump chamber, and the second air bleeding hole has a diameter smaller than that of the first air bleeding hole. It is therefore possible to prevent the cooling water flowing in the bypass passage from flowing in the pump chamber of the water pump through the air bleeding hole. Thus, it is possible to prevent the air bled from the cooling water can be prevented from returning in the pump chamber of the water pump.

Preferably, the first air bleeding hole is formed by casting and the second air bleeding hole is formed by machining. Therefore, the manufacturing of the air bleeding hole can be reduced to the minimum, thereby providing reduced manufacturing costs.

Brief Description of the Drawings Preferred embodiments of the invention will be described hereinafter, by way of examples only, with reference to the accompanying drawings, in which: [R:*LIBLL] I 8250.doc:JPH -4- Fig. 1 is a lateral view of a vehicle on which an air bleeding structure of a water-cooled internal combustion engine is mounted according to a preferred embodiment of the present invention; Fig. 2 is a plan view of the vehicle depicted in Fig. 1; Fig. 3 is a cross-sectional view for illustrating the air bleeding structure for the internal combustion engine according to a preferred embodiment of the invention, taken along a line connecting a cylinder head, a cylinder block, a crankshaft, a main shaft, a counter shaft, an intermediate shaft, and a differential included in a power unit; Fig. 4 is a cross-sectional view taken along a face passing the respective axes of a fork shaft, the main shaft, a reverse shaft, the counter shaft and the fork shaft included in the power unit shown in Fig. 3; Fig. 5 is a partial cut-away side view of the left crankcase of the power unit shown in Fig.

3 as viewed from the inside thereof; Fig. 6 is a partial cut-away side view of the left crankcase of the power unit shown in Fig.

3 as viewed from the outside thereof; and Fig. 7 is a partial cut-away cross-sectional view for explaining a thermostat valve of the power unit shown in Fig. 3.

[R:¥LIBLL] I 8250.doc:JPH Preferred Embodiments of the Invention Figs. 1 through 7 show the embodiment of the invention. Fig. 1 is a side view of a vehicle on which an air bleeding structure for a water-cooled internal combustion engine according to the invention is mounted. Fig. 2 is a plan view of the vehicle depicted in Fig. 1. Fig. 3 is a cross-sectional view for illustrating the air bleeding structure according to the invention, taken along a line connecting a cylinder head, a cylinder block, a crankshaft, a main shaft, a counter shaft, an intermediate shaft, and a differential included in a power unit. Fig. 4 is a cross-sectional view taken along a face passing the respective axes of a fork shaft, the main shaft, a reverse shaft, the counter shaft and the fork shaft included in the power unit shown in Fig. 3. Fig. 5 is a partial cut-away side view of a left crankcase of the power unit shown in Fig. 3 as viewed from the inside thereof. Fig. 6 is a partial cut-away side view of the left crankcase of the power unit shown in Fig. 3 as viewed from the outside thereof. Fig. 7 is a partial cut-away crosssectional view for explaining a thermostat valve of the power unit shown in Fig. 3.

It is to be noted that in Figs. 1 and 2 "front", "rear" "left" and "right" mean respective directions with respect to the driver and symbol Fr denotes the front, Rr the rear, L the left and R the right.

In Figs. 1 and 2 a small-sized four-wheeled automobile or the vehicle 10 includes a vehicle body (body frame) 11, two front wheels 12, 12 and two rear wheels 13, 13 attached to the body frame, and a steering mechanism 14 having a handlebar 15 attached to the front portion of the body frame 11. In addition, the vehicle includes a front seat 16 and a rear seat 17 placed at the middle portion of the body frame 11 and a power unit (internal combustion engine) 1 rearward below the body frame 11. Further, the vehicle includes: a front cover 18 which covers the periphery of the front portion of the body [RAULBLLJ I 8250.doc:JPH frame 11; a windscreen 19 which is attached to the upper portion of the front cover 18; a roof 20 which continuously extends rearward from the upper end of the window screen 19 to cover the front and the rear seat 16, 17 from above; and a rear cover 21 which covers the rear portion of the body frame 11.

The supporting structure of the roof 20 is such that the roof 20 is supported by left and right roof side pillars 22, 22. The roof side pillars 22, 22 are pipe-like roof pillars which extend from the front portion of the body frame to the rear portion thereof in arched, curved form. The roof side pillars have a structure of combining the front pillars 23, 23 1o with the rear pillars 24, 24.

In the front portion of the body frame, the left and right front pillars 23, 23 extend rearward upward from the upper end of the front cover 18 and a front cross member 25 is spanned between the respective upper ends of the front pillars 23, 23. The windscreen 19 is provided between the front pillars 23, 23.

The left and right rear pillars 24, 24 extend upward from the upper ends of left and right supporting members 26, 26, respectively, provided in the rear portion of the body frame.

In addition, they extend further forward from the upper ends and the front ends thereof are detachably bolted to the rear ends of the front pillars 23, 23. A rear cross member 27 is spanned between the rear upper ends of the rear pillars 24, 24. The left and right supporting members 26, 26 are bolted at its upper ends to the left and right rear pillars 24, 24, respectively, for detachable support.

[R:*LIBLL]I 8250.doc:J PH -7- A frame is composed of the left and right front pillars 23, 23, the left and right rear pillars 24, 24, and the front and rear cross members 25, 27. An almost-flat-plate-like roof 20 is detachably attached to the frame. The roof 20 can be supported in this way.

s The rear end of the roof 20 is rearward of the rear seat 17. The roof 20 has a width almost-equal to or slightly smaller than the vehicle width. The sides of the vehicle are open so that a driver or a rear passenger can freely get on and off therefrom.

In this way, the front of the front seat 16 can be covered by the windscreen 19 and the io upside of the front seat 16 and that of the rear seat 17 can be covered by the roof Consequently, the rear passenger as well as the driver can be protected from rain or the like. It is advantageous for rain or the like to put baggage on the rear seat 17. Since only the roof 20 is provided and the sides are open, the driver or rear passenger can easily get on and off in spite of the presence of the roof The vehicle 10 includes a shift lever 28, a parking lever 29, a headlamp 30, turn signal lamps 31, side mirrors 32, front fenders 33, 33, rear fenders 34, 34, an accelerator pedal (not shown) and a brake pedal (not shown).

As shown in Fig. 3, the power unit 1 is a water-cooled 4-stroke cycle single-cylinder internal combustion engine. As shown in Fig. 1, the power unit 1 is mounted on the vehicle 10 so that a crankshaft's axis may be perpendicular to the traveling direction of the vehicle and the cylinder axis may be almost-horizontal relative to the traveling direction so as to cause the cylinder head to face forward.

[R:¥LIBLL] I 8250.doc:JPH -8- As shown in Fig. 3, the power unit 1 has an outer shell configured by connecting a left crankcase 2, a right crankcase 3, a cylinder block 40, a cylinder head 50, a left crankcase cover 60, a right crankcase cover 61, and an intermediate gear housing case cover 62.

The left and right crankshafts 2, 3 are joined together to define a crankcase 4. A crankshaft 100, a transmission 200 and a differential 300 are disposed in the crankcase 4.

Incidentally, the left crankcase cover 60 is bolted to the left side face of the left crankcase 2 and the right crankcase cover 61 is bolted to the right side face of the right crankcase 3.

The left crankcase 2 includes an intermediate gear housing case 5 formed to dispose a io first intermediate gear 202a and a second intermediate gear 203a therein, that is, in a case separate from the crankcase 4. The first intermediate gear 202a is secured to a counter shaft 202 of the incorporated transmission 200. The second intermediate gear 203a is secured to an intermediate shaft 203. The intermediate gear housing case 5 is formed by allowing a circumferential wall 2c to project outward from the left crankcase 2 so as to surround both the intermediate gears 202a, 203a. In addition, an opening portion of the intermediate gear housing case 5 is closed by an intermediate gear housing cover 62 bolted to the left crankcase 2.

The cylinder head 50 is co-fastened with the cylinder block 40 with stud bolts 45. The cylinder block 40 is inserted into an opening defined at the upper portion of the left and right crankcases 2 and 3 coupled together. A combustion chamber 51 is formed below the cylinder head 50 and a spark plug 52 is attached to the cylinder head 50 so as to face the combustion chamber 51.

The camshaft 53 of a valve train is rotatably supported in the cylinder head 50 and a cam sprocket 54 is secured to an end of the camshaft 53. A cam chain 94 is spanned between [R:ALIBLL] I 8250.doc:J PH -9the cam sprocket 54 and a driving sprocket 102 secured to the crankshaft 100. With this configuration, a rotary-driving force of the crankshaft 100 is transmitted to the camshaft 53 to drive a rocker arm 55 disposed on the cylinder head 50, thereby opening and closing an intake valve and an exhaust valve, not shown, in the combustion chamber at the right moment.

A cooling water circulation mechanism 150 is provided on the left of the cylinder head This mechanism 150 is mainly composed of a water pump 151, a thermostat valve 152 and a radiator, not shown, disposed at the front portion of the vehicle 10 (refer to Fig. 1).

to The water pump 151 has a pump shaft 158 which is connected at its right end to the left end of the camshaft 53 included in the valve train. The pump shaft 158 is rotated by the rotation of the camshaft 53 to operate the water pump 151.

A water jacket 58 is formed at a portion of the cylinder head 50 above and near the combustion chamber 51. Another water jacket 44 is formed at a portion of the cylinder block 40 near the combustion chamber 51 to surround it. The cylinder head 50 and the cylinder block 40 are coupled together to cause both the water jackets 44, 58 to communicate with each other.

The crankshaft 100 is composed of left and right parts, which are united by a crankpin 101. The crankshaft 100 is rotatably carried by roller bearings 70 and 71 disposed in the left and right crankcases 2 and 3, respectively. An alternator 90 and a torque converter 91 are mounted onto the axial left portion and axial right portion, respectively, of the crankshaft 100. A piston 42 is connected to the crankpin 101 via a connecting rod 41 and reciprocated in an cylinder-axial direction within a cylinder liner 43, which is formed in the cylinder block 40 by integral molding therewith.

[RAULBLLI I 8250.doc:JPH The alternator 90 generates high voltage applied to the spark plug 52 via an ignition coil (not shown) and also current charged to a battery (not shown).

The torque converter 91 includes: a pump impeller 91a spline-connected to the crankshaft 100; a turbine runner 91b disposed opposite the pump impeller 91a; a stator 91d connected to the crankshaft 100 via a one-way clutch 91c; and a stator-fixing plate 91e receiving a reaction force applied to the stator 91d.

1o The torque converter 91 is filled with torque converter oil serving also to lubricate the crankcase 4. In the torque converter 91, when the pump impeller 91a rotates together with the crankshaft 100 and the turbine runner 91b does not follow the pump impeller 91a, the stator 91d receives a reaction force acting in a direction opposite to the rotating direction of the pump impeller 91a. Then the stator-fixing plate 91e receives the reaction force. The rotary power of the turbine runner 91b is transmitted to a primary driven gear 93 of a multiple disk clutch 92 via a primary driving gear 103. The multiple disk clutch 92 is attached to the right portion of the main shaft 201. The primary driving gear 103 is externally carried on the crankshaft 100.

The multiple disk clutch 92 is a wet shift-change clutch, which is mounted to the right portion of the main shaft 201. The multiple disk clutch 92 includes, in an outer case 92a, a plurality of clutch plates 92b, and a plurality of clutch disks 92c alternately disposed between the clutch plates 92b. In addition, the clutch 92 incorporates a damper spring, a drive plate, a stop ring, a clutch spring, a clutch weight, an outer drive gear, a center clutch, a free spring and a set ring, which are not shown in the figure. In addition, a clutch lifter lever (not shown) is connected to a change spindle carried by the right [R:¥LIBLL] 18250.doc:JPH 11 crankcase 3 and a clutch lifter cam plate (not shown) is attached to the clutch 92. If the clutch lifter lever rotates the clutch lifter cam plate, the multiple disk clutch 92 brings the transmission 200 into a neutral state without transmitting the rotary power of the crankshaft 100 during the gear shift in the transmission 200 and transmits the rotary power of the crankshaft 100 to the transmission 200 simultaneously with the completion of the gear shift in the transmission 200.

As shown in Figs. 3 to 5, the transmission 200 includes the main shaft 201, the counter shaft 202, the intermediate shaft 203, a reverse shaft 204, a fork shaft 205, and a shift drum 206, which are disposed parallel to the crankshaft 100. Incidentally, Fig. 4 is a cross-sectional view taken along a line joining the fork shaft 205, the main shaft 201, the reverse shaft 204, the counter shaft 202, and the fork shaft 205, that is, the two fork shafts 205 are depicted. However, the fork shaft 205 is a single one in fact.

The main shaft 201 is rotatably supported by the left and right crankcases 2 and 3 through roller bearings 72 and 73 disposed thereon, respectively. The main shaft 201 includes gears 201a, 201b fitted relatively rotatably thereto, a gear 201c, and a gear 201d formed integral therewith. The gear 201c is retained in a rotary direction between the gears 201a and 201b so as to be slidably movable in the axial direction of the main shaft 201. In addition, the gear 201c can be engaged with the gear 201a or the gear 201b by moving a first shift fork 207.

The counter shaft 202 is rotatably supported by the left and right crankcases 2 and 3 through roller bearings 74 and 75 disposed thereon, respectively. The counter shaft 202 includes a gear 202b secured thereto, gears 202c, 202d fitted relatively rotatably thereto, and a gear 202e. The gear 202e is retained in rotary direction between the gears 202c [R:,YLIBLL] I 8250.doc:JPI-I 12and 202d so as to be slidably movable in the axial direction of the counter shaft 202. In addition, the gear 202e can be engaged with the gear 202c or the gear 202d by moving a second shift fork 208. A first intermediate gear 202a (refer to Fig. 3) is secured to the left end of the counter shaft 202 so as to be disposed within the intermediate gear housing case The intermediate shaft 203 is rotatably supported by the left and right crankcases 2 and 3 through roller bearings 76 and 77 disposed thereon, respectively. The intermediate shaft 203 includes a second intermediate gear 203a secured at the left end thereof and a gear 203b biased leftward by a spring mechanism 209 to be retained in a rotary direction.

The second intermediate gear 203a is disposed within the intermediate gear housing case whereas the gear 203b is disposed within a differential case 301. This differential case 301 is formed, in the crankcase 4 rearward of the transmission 200, independently of the crankcase 4 and the intermediate gear housing case 5 through partition walls 6 and 7 in the left and right crankcases 2 and 3, respectively. Incidentally, the first intermediate gear 202a is always in meshing engagement with the second intermediate gear 203a.

The reverse shaft 204 is supported by respective fitting portions formed at the left and right crankcases 2 and 3 and rotatably supports gears 204a and 204b which are formed integral with each other.

The fork shaft 205 is supported by respective fitting portions formed at the left and right crankcases 2 and 3. The fork shaft 205 supports a first shift fork 207 and a second shift fork 208 so as to be slidably movable in the axial direction thereof.

[RXL1B LL] I 8250.doc:J PH 13 The shift forks 207, 208 are respectively inserted to cam grooves provided on the shift drum 206. Thus, when the shift drum 206 is rotated, the shift forks 207, 208 slide on the axis of the fork shaft 205 along the respective cam grooves 206a, 206b.

The differential 300 is disposed within the differential case 301. Since a ring gear 302 is in meshing engagement with the gear 203b of the intermediate shaft 203, the rotary power of the intermediate shaft 203 is transmitted to the ring gear 203b through the gear 203b, whereby a differential gear unit 303 rotates the left and right drive shafts 304, 305.

io As shown in Fig. 5, an injector 59 is attached to the upper portion of the cylinder head The injector 59 is electrically connected to an engine control unit not shown. The injector 59 injects high-pressurized fuel to an intake port not shown by an electric current supplied from the engine control unit in response to engine speed.

The left and right crankcases 2 and 3 are formed in the split surfaces thereof with lubricating oil-feeding passages 2a, respectively, in a symmetrical manner. The passages 2a are closed by joining both the crankcases 2, 3 together. The passage 2a is connected at the front end thereof to the discharge end of an oil pump (not shown) to communicate therewith. In addition, the passage is connected at the rear end thereof to the oil-feeding passage 5a (see Fig. 6) of the intermediate gear housing case 5 to communicate therewith.

As shown in Fig. 6, the intermediate gear housing case 5 is formed by allowing the circumferential wall 2c surrounding both the intermediate gears 202a, 203a to protrude from the left crankcase 2 outward. The circumferential plate 2c is formed on its end face with the oil-feeding passage 5a having an almost-inverse-L shape as viewed laterally.

The oil-feeding passage 5a includes: a middle hole 5b communicating with the oil- [R:,YLIBLL] I 8250.doc:JPH -14feeding passages 2a, 3a; a main shaft hole 5c provided below the middle hole 5b; a reverse shaft hole 5d provided rearward of the middle hole 5b; and connection grooves one of which connects the middle hole 5b with the main shaft hole 5d and the other of which connects the middle hole 5b with the reverse shaft hole 5d. In addition, the main shaft hole 5c and the reverse shaft hole 5d pass through the end face of the circumferential plate 2c and reach the inside of the crankcase 4.

An orifice hole 2d is bored to pass through the left crankcase 2 so as to be open to the intermediate gear housing case 5 at a position adjacent to the main shaft hole 5c. As 1o shown in Fig. 3, the orifice hole 2d communicates with the oil-feeding passage 5a through the main shaft hole 5c and also with a lubricating oil passage 201e (refer to Fig. 3) formed within the main shaft 201. In addition, a lubricating oil return hole 2e is bored to pass through the crankcase 4 so as to be open to the intermediate gear housing case 5 at a position on the rear side of the first intermediate gear 202a.

An intermediate gear housing case cover 62 is mounted to the intermediate gear housing case 5 to block the openings and close the oil-feeding passage 5a. The lubricating oil discharged from the orifice hole 2d is pooled on the bottom of the circumferential plate 2c while lubricating the first and the second intermediate gear 202a, 203a by the bathtub method. Thereafter, the lubricating oil that has been pooled on the bottom of the circumferential plate 2c is returned from the lubricating oil return hole 2e to the crankcase 4.

Accordingly, one portion of the lubricating oil discharged from the oil pump is supplied to the lubricating hole 105 of the crankshaft 100 through the oil-feeding passage (not shown) formed in the crankcase cover 61. In addition, the other portion is supplied to the oil- [R:ALIBLL] 18250.doc:JPH 15 feeding passage 2a formed in the respective split surfaces of the left and right crankcases 2 and 3. The lubricating oil supplied to the lubricating hole 105 is fed to the crankpin 101 through the torque converter 8.

The lubricating oil supplied to the oil-feeding passage 2a formed in the left and right crankcases 2, 3 is supplied from the front end of the oil-feeding passage 2a to the rear end thereof. In the oil-feeding passage 5a of the intermediate gear housing case 5, then, the lubricating oil is caused to flow from the middle hole 5b to the main shaft hole 5c and the reverse shaft hole 5d. The lubricating oil supplied to the main shaft hole 5c is fed therefrom to the left bearing 72 of the main shaft 201. Then the lubricating oil is once taken into the lubricating oil passage 201e (see Fig. 3) formed within the main shaft 201, supplied to the orifice hole 2d, and discharged therefrom to the intermediate gear housing case On the other hand, the lubricating oil supplied from the middle hole 5b to the reverse shaft hole 5d is fed therefrom to the left portion of the reverse shaft 204. Then it is fed to the lubricating oil passage 204c (see Fig. 4) formed in the reverse shaft 204. The lubricating oil pooled in an oil pocket 3c formed in the right crankcase 3 is fed to the lubricating hole 202f (see Fig. 4) formed in the counter shaft 202.

The cooling water circulation mechanism 150 is then detailed with reference to Figs. 3 and 5 to 7.

The cooling water circulation mechanism 150 is mainly composed of the water pump 151, the thermostat valve 152 and the radiator, not shown, disposed at the front portion of the vehicle 10 (refer to Fig. The water pump 151 is incorporated in a water pump [R:N;LIBLL] I 8250.doc:J PH -16housing (the housing for the water pump) 153. A thermostat case (the housing for the thermostat valve) 155 for the thermostat valve 152 is integrally bolted to the water pump housing 153. The thermostat valve 152 has a bypass passage 154.

The water pump 151 is rotatably supported by roller bearings 78 disposed at the water pump housing 153. The water pump 151 includes a pump shaft 158 connected to the left end of the cam shaft 53, a rotary blade (impeller) 157 formed integral with the pump shaft 158, and a seal member 79 (refer to Fig. The water pump housing 153 and the thermostat case 155 are bolted integrally to each other to define a pump chamber 156, in which the rotary blade 157 is disposed.

The thermostat valve 152 is housed in a thermostat chamber 159, which is defined by the thermostat case 155 and a cover 165 bolted integrally to each other. The cover 165 is formed with a radiator water inlet nozzle 164 to be connected to a radiator hose 162 communicating with the radiator. The thermostat case 155 is formed with the bypass passage 154 and a cooling water inflow passage 160. This inflow passage 160 causes the pump chamber 156 to communicate with the thermostat chamber 159. In addition, the thermostat case 155 is formed with an air bleeding hole 170, which intersects the bypass passage 154 and causes the bypass passage 154 to communicate with the pump chamber 156. In addition, a bypass water inlet nozzle 154a is fitted into the bypass passage 154.

The water pump housing 153 is joined integrally to the thermostat case 155 to define a cooling water discharge port 161 communicating with the pump chamber 156. The cooling water discharge port 161 is made to communicate with the water jacket 44 of the cylinder block 40 through a water jacket hose 163 and a water jacket inlet nozzle 166 [R:ALIBLI] I 8250.doc:JPH 17bolted to the lower surface of the cylinder block 40. The water jacket 44 communicates with the water jacket 58 of the cylinder head 50 (see Fig. The water jacket 58 communicates with a cooling water distributing unit 167 bolted to the right surface of the cylinder head 50. A radiator hose not shown used to supply cooling water to the radiator and a bypass hose 168 communicating with the bypass water inlet nozzle 154 are connected to the cooling water distributing unit 167. In addition, an air bleeding valve 169 is provided at the upper end of the cooling water distributing unit 167 so as to bleed the residual air within the cooling water circulation mechanism 150.

The thermostat valve 152 is fixed by sandwiching in a bridge plate portion 152a between the water pump housing 153 and the thermostat case 155. A spring support member 152b is attached to the bridge plate portion 152a. The bridge plate portion 152a holds one end of a plunger 152d projecting from a cylindrical movable portion 152c. The other end of the plunger 152d is inserted into the cylindrical movable portion 152c. The cylindrical movable portion 152c functions as a temperature sensing portion since it has wax encapsulated within the enlarged part thereof. The cylindrical movable portion 152c includes a first valve body 152e and a second valve body 152f. The first valve body 152e is secured to the cylindrical movable portion 152c. The second valve body 152f is biased by a conical coil spring 152g extending from the cylindrical movable portion 152c and is disposed to face the bypass passage 154. A coil spring 152h is attached between the spring support member 152b and the first valve body 152e. Further, the bridge plate portion 152a is formed with a small opening portion 152j associated with a jiggle valve 152j. The jiggle valve 152j moves downward due to the gravity to open the small opening portion 152i during pour of cooling water so that the air in the radiator hose 162 may move into the thermostat chamber 159. On the other hand, the jiggle [R:ALIILL) I 8250.doc:JPH 18valve 152j is lifted by the water pressure of the water pump 151 to close the small opening portion 152i during the operation of the engine.

The air bleeding hole 170 includes a first air bleeding hole 171 communicating with the bypass passage 154 and a second air bleeding hole 172 allowing the first air bleeding hole 171 to communicate with the pump chamber 156. The first air bleeding hole 171 is tapered by casting. The second air bleeding hole 172 is formed to have a diameter smaller than the inner diameter of the first air bleeding hole 171 by machining such as drilling or the like. The air bleeding hole 170 is open above the left end face of the 1o pump chamber 156. Incidentally, the outer opening of the air bleeding hole 170 is closed with a plug 173.

With the cooling water circulation mechanism 150 configured described above, when cooling water is poured into the radiator from the upper portion thereof, such as when cooling water is changed, air will remain in the thermostat chamber 159, the pump chamber 156 and the water jackets 44, 58. In this case, the power unit I is started up to rotate the cam shaft 53, and along with this rotation the rotary blade 157 of the water pump 151 starts to rotate. At this time, since the power unit 1 is not yet warmed-up, that is, cooling water is at low temperatures, the thermostat valve 152 causes the second valve body 152f to open the bypass passage 154 and the first valve body 152e to close between the bridge plate portion 152a and the first valve body 152e. Thus, the cooling water discharged from the pump chamber 156 by the operation of the water pump 151 is circulated through the cooling water circulation mechanism 150 in the following order: the pump chamber 156, the cooling water discharge port 161, the water jacket hose 163, the water jacket inlet nozzle 166, the water jackets 44, 58, the cooling water distribution unit 167, the bypass hose 168, the bypass passage 154, the thermostat chamber 159, the [R:.YLIBLL] I 8250.doc:JPHl 19cooling water inflow passage 160, and the pump chamber 156. Incidentally, although the first valve body 152e of the thermostat valve 152 is closed, the jiggle valve 152j prevents a small amount of cooling water from flowing in the thermostat chamber 159 from the radiator.

In this case, the residual air in the pump chamber 156 collects first at the upper portion of the pump chamber 156, moves from the second air bleeding hole 172 to the first air bleeding hole 171, and further moves along the tapered surface of the first air bleeding hole 171 to inside the bypass passage 154. On the other hand, the residual air in the thermostat chamber 159 moves to the bypass passage 154 disposed at a position higher than the thermostat chamber 159. The residual air that has moved in the bypass passage 154 moves along the inner circumferential surface of the sloped bypass hose 168 in a direction reverse to the flow of the cooling water. Lastly, the residual air is discharged to the outside from the air bleeding valve 169 disposed at the upper end of the cooling water distribution unit 167. Further, the air remaining between the water jacket inlet nozzle 166 and the cooling water distribution unit 167 moves in the same direction as that of the cooling water flow and then is discharged from the air bleeding valve 169.

When the power unit 1 is warmed up along with the elapse of time after the starting-up, so that cooling water reaches a specified temperature, the cylindrical movable portion 152c of the thermostat valve 152 rises in temperature to expand the wax encapsulated therein. Consequently, the cylindrical movable portion pushes out the plunger 152d.

Since the plunger 152d is retained at its tip to the bridge plate portion 152a, then, based on its reactive force the cylindrical movable portion 152c itself moves against the elastic repulsive force of the coil spring 152h to open the first valve body 152e and close the second valve body 152f. In this way, the cooling water that has been discharged from [R:NLIB LLJ I 8250.doc:JPH 20 the pump chamber 156 is circulated within the cooling water circulation mechanism 150 in the following order: the pump chamber 156, the cooling water discharge port 161, the water jacket hose-163, the water jacket inlet nozzle 166, the water jackets 44, 58, the cooling water distribution unit 167, the radiator hose (not shown), the radiator (not shown), the radiator hose 162, a radiator water inlet nozzle 164, the thermostat chamber 159, the cooling water inflow passage 160, and the pump chamber 156.

With the air bleeding structure of the water-cooled internal combustion engine described above, the thermostat case 155 is provided with the air bleeding hole 170 which intersects the bypass passage 154 and causes the bypass passage 154 to communicate with the pump chamber 156 of the water pump 151. Therefore, air in the pump chamber 156 of the water pump 151 and in the thermostat case 155 can be bled in a collective manner. Thus, it is not necessary to additionally provide a passage, a joint and the like used to bleed air, for the water pump housing 153. This allows the internal combustion engine to have a simple configuration, and reduces the number of man-hour for machining and the like and the number of components, thereby providing reduced manufacturing costs.

With the air bleeding structure of the water-cooled internal combustion engine described above, the air bleeding hole 170 includes the first air bleeding hole 171 communicating with the bypass passage 154 and the second air bleeding hole 172 allowing the first air bleeding hole 171 to communicate with the pump chamber 156. In addition, the second air bleeding hole 172 has a diameter smaller than that of the first air bleeding hole 171.

It is therefore possible to prevent the cooling water flowing in the bypass passage 154 from flowing in the pump chamber 156 of the water pump 151 through the air bleeding hole 170. Thus, the air bled from the cooling water can be prevented from returning in the pump chamber 156 of the water pump 151.

[R:*LIBLL] I 8250.doc:JPH -21 Further, with the air bleeding structure of the water-cooled internal combustion engine described above, the first air bleeding hole 171 is formed by casting and the second air bleeding hole 172 is formed by machining; therefore, the manufacturing of the air bleeding hole 170 can be reduced to the minimum, thereby providing reduced manufacturing costs.

While the invention has been described with reference to specific embodiments, it will be appreciated that it may also be embodied in many other forms.

[R:¥LIBLL] 18250.doc:JPH

Claims (4)

1. An air bleeding structure for a water-cooled internal combustion engine in which a water pump is attached integrally to one end of a camshaft provided in a cylinder head and a thermostat valve housing with a bypass passage is joined integrally to a housing for the water pump, wherein the air bleeding structure is provided with an air bleeding hole which intersects the bypass passage and allows the bypass passage to communicate with a pump chamber of the water pump.

2. The air bleeding structure for a water-cooled internal combustion engine according to claim 1, wherein the air bleeding hole includes a first air bleeding hole communicating with the bypass passage and a second air bleeding hole allowing the first air bleeding hole to communicate with the pump chamber, and the second air bleeding hole has a diameter smaller than that of the first air bleeding hole.

3. The air bleeding structure for a water-cooled internal combustion engine according to claim I or 2, wherein the first air bleeding hole is formed by casting and the second air bleeding hole is formed by machining. [R:*LIBLL] I 8250.doc:JPH 23

4. An air bleeding structure for a water-cooled internal combustion engine in which a water pump is attached integrally to one end of a camshaft provided in a cylinder head and a thermostat valve housing with a bypass passage is joined integrally to a housing for the water pump, said air bleeding structure substantially as hereinbefore described with reference to any one of the embodiments, as that embodiment is shown in the accompanying drawings. Dated 3 March, 2006 Honda Motor Co., Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:¥LIBLL] I 8250.doc:JPH