Portable Generator

1. Field of the Invention

The present invention relates to a portable generator having an engine and a generator body driven by the engine and accommodated within a sound insulating case together with the engine.

2. Description of the Prior Art

In general, portable generators include a generator body driven by an engine. Most of the portable generators have a sound insulating case within which the engine and its peripheral components are accommodated to reduce noise resulting from operation of the engine. The engine and a muffler heated by engine exhaust gases constitute a heat generating component. In order to accommodate such heat generating component within the sound insulating case, appropriate measures should be taken to cool the heat generating component.

One example of such portable generators is known from Japanese Utility Model Publication No. SHO 64-3777. The known portable generator includes a sound insulating case composed of a base, a main cover secured to the base along opposite longitudinal edges, and two side covers closing opposite ends of the main cover. Within the sound insulating case, an engine, a generator body and a muffler are accommodated. The engine has a cooling fan. The engine and the cooling fan are covered by an engine cover. The engine cover is covered by a shroud. The generator body and the muffler are covered by a duct. The duct is connected to the shroud, and the shroud is connected to the engine cover. The respective internal spaces of the engine cover, shroud and duct communicate with each other. Thus, by the engine cover, shroud and duct is formed a ventilating duct extending from an intake hole formed in the engine cover to an exhaust hole formed in the sound insulating case.

In the known portable generator of the foregoing construction, outside air is introduced into the sound insulating case from a plurality of air intake holes formed in the base. A part of the outside air is drawn into a cylinder of the engine for combustion, and exhaust gases are discharged from the muffler to the outside of the generator. By the cooling fan driven by the engine, another part of the outside air is drawn into the engine cover, then forced to flow downstream through the shroud and the duct to cool the engine and the muffler, and finally exhausted from vent holes formed in the side cover.

In the aforesaid forced air-cooling system where the outside air is forced against the outside surface of the engine to cool the same, increase of the cooling efficiency requires either enlargement of the surface area (cooling area) of the engine, or increase of the quantity of outside air forced against the engine. In general, there is a limit to which extent the engine surface area can be enlarged. Accordingly, the second alternative (i.e., increase of the outside air quantity) is usually chosen. However, in order to increase the quantity of outside air, a larger cooling fan is needed and, hence, upsizing of the portable generator is not avoidable.

With the foregoing problem in view, it is an object of the present invention to provide a portable generator having structural features which enable highly efficient cooling of the interior of a sound insulating case while providing enhanced sound-insulating effect, without incurring upsizing of the generator.

To attain the foregoing object, a portable generator according to the present invention comprises: an engine; a generator body driven by the engine; a sound insulating case which contains the engine and the generator body; a cooling and ventilating shroud made of metal and surrounding at least a crankcase and a cylinder block of the engine; the engine being directly mounted to a portion of the shroud; and the shroud being connected to the sound insulating case through a vibration-proof member so that the shroud is accommodated within the sound insulating case.

Since the engine is directly mounted to the metal shroud, the shroud forms an additional cooling area of the engine to thereby increase the radiating surface of the engine. Heat from the engine while running is directly transferred to the metal shroud and radiated therefrom, so that the engine is cooled efficiently. Additionally, because the shroud surrounding at least the crankcase and cylinder block of the engine is accommodated within the sound insulating case, the portable generator has a double sound-insulating structure. With this double sound-insulating structure, noise resulting from operation of the engine is reduced greatly. Vibrations generated while the engine is running are effectively damped by the vibration-proof member before they are transmitted to the sound insulating case. The vibration-proof member is preferably made of rubber.

In one preferred form of the invention, the generator body is disposed on an inlet side of the shroud, and a muffler of the engine is disposed on an outlet side of the shroud. The generator body is a permanent-magnet outer roller generator having an outer rotor driven for rotation by the engine, and a cooling fan mounted attached to the outer rotor. Rotation of the cooling fan causes outside air to be drawn into the sound insulating case from an inlet thereof. The outside air is then drawn into shroud, forced to flow downstream through the shroud to successively cool the engine and the muffler, and finally exhausted from the sound insulating case. This cooling system has only one cooling fan but can cool the generator body, engine and muffler with improved efficiency.

Preferably, the shroud is a split shroud composed of right and left shroud halves of metal plate joined together at an upper and a lower end portion of the shroud. Each of the joined upper and lower end portions of the split shroud is connected to the case via the vibration-proof member. Use of the split shroud makes shrouding or encasing process of the engine ease.

The above and other objects, features and advantages of the present invention will become manifest to those versed in the art upon making reference to the detailed description and accompanying sheets of drawings in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative examples.

FIG. 1 is a perspective view of a portable generator according to an embodiment of the present invention;

FIG. 2 is a vertical cross-sectional view of the portable generator shown in FIG. 1;

FIG. 3 is a side view, with parts in cross section, of a generator unit of the portable generator shown in FIG. 2;

FIG. 4 is an exploded perspective view of the generator unit shown in FIG. 3;

FIG. 5 is an enlarged cross-sectional view taken along line V--V of FIG. 2;

FIG. 6 is an enlarged cross-sectional view showing a shroud hanger attachment structure shown in FIG. 5;

FIG. 7 is an enlarged cross-sectional view taken along line VII--VII of FIG. 2;

FIG. 8 is an enlarged cross-sectional view taken along line VIII--VIII of FIG. 2;

FIGS. 9A, 9B and 9C are diagrammatical views showing the relationship between a sound insulating case and the generator unit;

FIG. 10 is an enlarged cross-sectional view taken along line X--X of FIG. 2;

FIG. 11 is an exploded perspective view of a right intermediate cushion member piece and its peripheral components shown in FIG. 10;

FIG. 12 is an exploded perspective view illustrative of the manner in which the portable generator of FIG. 2 is assembled;

FIG. 13 is a diagrammatical view showing the flow of cooling air inside the portable generator shown in FIG. 2; and

FIG. 14 is a fragmentary side view showing a modified form of the carrying handle of the portable generator shown in FIG. 1.

Certain preferred structural embodiments of the present invention will be described below in greater detail with reference to the accompanying sheets of drawings. In some drawing figures, profiled arrows Fr, Rr, L and R are used to indicated respectively the forward, rearward, leftward and rightward directions of a portable generator 1 embodying the present invention.

As shown in FIG. 1, the portable generator 1 has a sound insulating case 2. The sound insulating case 2 is made from a synthetic resin and has four legs 3 (two being shown) at the bottom adjacent to respective corners for setting or installation of the portable generator 1. A carrying handle 4 for enabling hand-carrying transportation of the portable generator 1 is formed integrally with a transverse central portion of the upper surf ace of the sound insulating case 2. The sound insulating case 2 has a front face on which a control panel 5 is provided. A plurality of air inlets 6 are formed in a front portion of each sidewall of the sound insulating case 2 for introducing outside air into the sound insulating case 2.

The sound insulating case 2 including the carrying handle 4 is composed of right and left case halves or members 2R, 2L that can be separated in the widthwise direction along a longitudinal parting line contained in a vertical plane. The right and left case members 2R, 2L are joined together by four screws (not shown), two of which are located at opposite end portions (rear and front end portions) A, B of the carrying handle 4 while the other two screws at a rear end portion C and an intermediate portion D of a lower part of the sound insulating case 2.

The carrying handle 4 has a generally inverted U shape elongated in the longitudinal direction of the sound insulating case 2 to secure adequate hand gripping by the user. The carrying handle 4 is composed of right and left handle halves or members 4R, 4L formed integrally with the right and left case members 2R, 2L, respectively.

In FIG. 1 reference numeral 7 denotes a side cover, and numeral 8 denotes a lid for enabling inspection of a spark plug.

As shown in FIG. 2, the sound insulating case 2 of the portable generator 1 accommodates within it a generator unit 10, a control unit accommodating box 72 and a fuel tank 74. The control unit accommodating box 72 and the fuel tank 74 are disposed forwardly of the generator unit 10.

FIGS. 3 and 4 show in detail the structure of the generator unit 10. As shown in these figures, the generator unit 10 generally comprises an engine 20, a base 11 for supporting thereon the engine 20, a muffler 32 connected through an exhaust pipe 31 to the engine 20, a generator body 33 assembled with the engine 20, a cooling fan 34 assembled with the generator body 33 and rotatable for drawing outside air, a recoil starter 36 connected by a connecting shaft 35 to the cooling fan 34, a fan cover 37 surrounding the generator body 33 and the cooling fan 34, and a cooling and ventilating shroud 38 covering or enclosing the engine 20 and a part of the muffler 32.

The base 11 is comprised of an elongated rectangular steel plate and secured by three bolts B1 to three legs 26 (two being shown) provided on the bottom of the engine 10. The base 11 has a pair of tubular members 62, 62 carried on its front and rear end portions for a purpose described below.

The engine 20 is a single cylinder valve-in-head engine and includes a crankcase 21, a cylinder block 22 and a head cover 23 assembled together. The engine 20 has an output shaft 24 extending horizontally. The crankcase 21 and the cylinder block 22 are bolted together along flanged mating surfaces 25 (FIG. 3) extending obliquely to an axis of the output shaft 24.

The muffler 32 has a generally box-like shape and is attached to a rear face of the cylinder block 22. The muffler 32 has an exhaust port 32a opening at a rear surface thereof.

The generator body 33 is a permanent-magnet outer rotor generator or magneto having an outer rotor 33c driven for rotation by the engine 20. Thus, the portable generator 1 is an engine-driven generator.

The generator body 33 includes a core 33a mounted to the cylinder block 22, a plurality of coils 33b wound around the core 33a, the aforesaid outer rotor 33c having a cup-shaped configuration and mounted on the output shaft 24 of the engine 20, and a plurality of permanent magnets 33d fixed to an inner circumferential surface of the cup-shaped outer rotor 33c.

The outer rotor 33c is designed to surround the core 33a and the coils 33b, and the cooling fan (fan rotor) 34 is carried on a front face of the outer rotor 33c. Since the outer rotor 33c to which the cooling fan 34 is attached is highly rigid and has a large diameter, the cooling fan 34 is allowed to have a large diameter and can be easily and reliably attached to the outer rotor 33c. The use of such large-diameter cooling fan 34 enable creation of a large quantity of air which is sufficient to cool the engine 20 and the generator body 33. Additionally, because the outer rotor 33c serves also as a flywheel of the engine 20, no separate flywheel is needed. The internal space of the sound insulating case 2 can, therefore, be reduced correspondingly, enabling downsizing of the portable generator 1 (FIG. 1).

The output shaft 24 of the engine 20, the outer rotor 33c, the cooling fan 34, and the recoil starter 36 are coaxial with each other. The outer rotor 33c has a ventilating hole 33e.

The fan cover 37 has a generally bowl-like shape and is attached to the engine 20 (more particularly, the crankcase 21 and the cylinder block 22) by a plurality of stud bolts B2. The bowl-shaped fan cover 37 has a circular air inlet 37a at the bottom (left end in FIGS. 3 and 4) for introducing air into the fan cover 37, and a recoil starter supporting cap 39 attached to the fan cover 37 in front of the air inlet 37a, there being a clearance (not designated) between the recoil starter supporting cap 39 and the fan cover 37 so that the air can be drawn into the fan cover 37 through the clearance and the air inlet 37a connected to the clearance. The bowl-shaped fan cover 37 has an air outlet 37b at the open top end (right end in FIGS. 3 and 4) for letting the air out from the fan cover 37. The air outlet 37b is directly connected to an inlet 38a of the shroud 38 by a fit joint formed between the open right end of the fan cover 37 and an open inlet side end (left end in FIGS. 3 and 4) of the shroud 38.

To secure efficient cooling of the engine 20 inside the sound insulating case 2 (FIG. 2) while providing enhanced sound insulating effect, the shroud 38 is so designed as to cover or enclose at least the crankcase 21 and the cylinder block 22 of the engine 20, and preferably substantially the whole body of the engine 20 as in the illustrated embodiment. The shroud 38 is formed from a steel plate and has high stiffness properties. The engine 20 is directly mounted to such stiff shroud 38 by means of a plurality of screws B4, B5, B6 and B7 in such a manner that it is accommodated within the shroud 38. Reference numeral 41 shown in FIG. 3 denotes a spark plug mounting socket.

The generator unit 10 has a hanger portion 42 at the top and a pair of front and rear base mounting portions 61, 61 at the bottom.

Referring back to FIG. 2, the hanger portion 42 of the shroud 38 is connected to a reinforced mounting portion 4a (root or base of the carrying handle 4) at a rear end of the inverted U-shaped carrying handle 4. The reinforced mounting portion 4a supports the generator unit 10 via the shroud 38 which serves also as a hanger for the generator unit 10.

The base 11 is attached to a lower portion of the case 2 via the base mounting portions 61, 61 so that the weight of the generator unit 10 is born by the lower portion of the case 2.

An exhaust duct 44 is attached to an exhaust hole 45 formed at a rear end of the case 2 and covers or encloses a part of the muffler 32. The exhaust duct 44 has a rear wall formed with a multiplicity of vent holes comprised of slits 44a for venting the air from the case 2, and an engine exhaust opening 44b for discharging the engine exhaust gases emitted from the exhaust port 32a of the muffler 32.

As shown in FIG. 5, the shroud 38 is a split two-piece shroud composed of right and left shroud halves or members 38R and 38L which can be separated in the widthwise direction along a longitudinal central parting line contained in a vertical plane. The right and left shroud members 38R, 38L have respective top and bottom portions mated together face to face and fastened together by a pair of screws B8, B8 (an upper one of the screws B8 being shown in FIG. 3). To secure the engine 20 inside the shroud 38, part of a sidewall of the shroud 38 is fastened by the screws B4, B5, B6, B7 to plural internally threaded projections 27 formed on the cylinder block 22 of the engine 20. Since the shroud 38 of steel plate has a large heat-transfer coefficient (thermal conductivity), and since the engine 20 is directly attached to the shroud 38, heat from the engine 20 while running can be smoothly and rapidly transferred to the shroud 38 and radiated therefrom. The shroud 38 is received in the case 2 with its hanger portion 42 attached to the case 2. In FIG. 5 designated by 46 is a carburetor equipped with a governor.

FIG. 6 shows an attachment structure of the hanger portion 42 of the shroud 38. As shown in this figure, the hanger portion 42 is attached to the case 2 by gripping the hanger portion 42 between the right and left handle members 4R, 4L at the reinforced mounting portion 4a formed by the root of the carrying handle 4.

More specifically, the hanger portion 42 includes a right hanging strip or lug 51R extending upwardly from an upper end portion of the right shroud member 38R, an annular right retaining portion 52R integral with the right hanging lug 51R and projecting therefrom in a lateral outward direction, an annular first right vibration-proof member 53R press-fitted with the right retaining portion 52R, a left hanging strip or lug 51L extending upwardly from an upper end portion of the left shroud member 38L, an annular left retaining projection 52L integral with the left hanging lug 51L and projecting therefrom in a lateral outward direction, an annular first left vibration-proof member 53L press-fitted with the left retaining projection 52L, a horizontal hanging pin 54 press-fitted in central holes 53a of the right and left vibration-proof members 53R, 53L while the right and left hanging lugs 51R, 51L are kept in face-to-face contact with each other, and a right washer 55R and a left washer 55L fitted around opposite end portions 54a, 54a of the hanging pin 54 to prevent the right and left vibration-proof members 52R, 52L from displacing off the right and left retaining projections 52R, 52L.

The opposite end portions 54a, 54a of the hanging pin 54 project from outer ends of the right and left vibration-proof members 53R, 53L. These end portions 54a, 54a serve as mounting legs for securing the generator unit 10 to the case 2 through the first vibration-proof members 53R, 53L, and so they are hereinafter referred to as "first legs 54a, 54a".

The right and left handle members 2R, 2L each have an integral tubular socket portion 4b projecting interiorly and horizontally from the reinforced mounting portion 4a for snugly receiving therein one of the first legs 54a, 54a.

In assembly, the socket portions 4b, 4b are forced to fit over the first legs 54a, 54a, so that the right and left hanging lugs 51R, 51L are supported by the socket portions 4b, 4b via the hanging pin 54 and the first right and left vibration-proof members 52R, 52L in such a manner that the hanging lugs 51R, 51L are gripped between opposed front ends of the socket portions 4b, 4b via the washers 55R, 55L and the vibration-proof members 53R, 53L. Thus, the case 2 can stably support the generator unit 10 (FIG. 5) by gripping the generator unit 10 via the vibration-proof members 53R, 53L.

The first right and left vibration-proof members 53R, 53L are formed from an elastic material such as rubber. Since the respective upper end portions of the right and left shroud members 38R, 38L of the shroud 38 are mounted to the case 2 via the first right and left vibration-proof members 53R, 53L, vibrations generated by the engine 20 (FIG. 5) while running are damped at an upper portion of the shroud 38 by means of the first right and left vibration-proof members 53R, 53L.

According to a modification of the present invention, the hanger portion 42 of the shroud 38 may be attached to the case 2 by fitting together the socket portions 4b, 4b of the case 2 and the first legs 54a, 54a of the hanger pin 54 with the first right and left vibration-proof members 53R, 53L each disposed between one of the socket portions 4b, 4b and a corresponding one of the legs 54a, 54a. Additionally, the right and left vibration-proof members 53R, 53L may be integral with each other.

Referring now to FIG. 7, there is shown a joint structure between the right and left handle members 4R, 4L. The joint structure includes a threaded fastener composed of a screw B9 and a nut B10. The screw B9 extends through the left handle member 4L and is threaded into a nut B10 which is embedded in the right handle member 4R. The joint structure using the threaded fastener B9, B10 is formed at each of the rear and front end portions A, B (FIG. 1) of the carrying handle 4.

FIG. 8 shows in detail the structure of the base mounting portions 61, 61 shown in FIGS. 2 and 3. As shown in this figure, each of the mounting portions 61 is comprised of the tubular member 62 carried on, and extending transversely of, the base 11, a pair of annular second right and left vibration-proof members 63R, 63L press-fitted in the opposite ends of the tubular member 62, a hollow or tubular support pin 64 press-fitted in respective central holes 63a, 63a of the second right and left vibration-proof members 63R, 63L, and a right washer 65R and a left washer 65L fitted around opposite end portions 64a, 64a of the support pin 64 to prevent removal of the second right and left vibration-proof members 63R, 63L from fitting engagement with the tubular member 62 and the support pin 64.

The opposite end portions 64a, 64a of the support pin 64 project from outer ends of the second right and left vibration-proof members 63R, 63L. The opposite end portions 64a, 64a serve as mounting legs for securing the base 11 to the case 2 (FIG. 2) via the second vibration-proof members 63R, 63L, and so they are hereinafter referred to as "second legs 64a, 64a".

The right and left case members 2R, 2L each have an integral tubular socket portion 4c extending interiorly and horizontally at a bottom portion 2B of the case 2 for fitting engagement with a corresponding one of the second legs 64a, 64a of the support pin 64. The bottom portion 2B has a relatively high stiffness.

In assembly, the socket portions 4c, 4c are forced to rit over the second legs 64a, 64a, so that the tubular member 62 is supported by the socket portions 4c, 4c via the support pin 64 and the second right and left vibration-proof members 63R, 63L in such a manner that the tubular member 62 is gripped between opposed front ends of the socket portions 4c, 4c via the washers 65R, 65L and the vibration-proof members 63R, 63L. Thus, the case 2 stably supports the generator unit 10 (FIG. 2) by gripping the generator unit 10 via the vibration-proof members 63R, 63L.

The second right and left vibration-proof members 63R, 63L are formed from an elastic material such as rubber. Vibrations generated from the engine 20 (FIG. 5) while running are damped at the bottom portion of the shroud 38 by means of the second right and left vibration-proof members 63R, 63L.

The base mounting portions 61 may be modified to include a pair of second right and left vibration-proof members (not shown) which are attached in advance to the socket portions 4c, 4c, respectively. The second legs 64a, 64a are fitted in the socket portions 4c, 4c with the vibration-proof members disposed therebetween.

The right and left case members 2R, 2L are joined together at the bottom portion 2B of the case by means of a threaded fastener which is composed of a screw B11 and a nut B12. The nut 12 is embedded in the socket portion 4c of the right case member 2R. The screw B11 extends through the socket portion 4c of the left case member 2L and the support pin 64 and is threaded into the nut B12 to fasten the right and left case members 2R, 2L. This joint structure using the threaded fastener B11, B12 is formed at each of the rear end and intermediate portions C, D (FIGS. 1 and 2) of the case 2.

FIGS. 9A-9C show the relationship between the case 2 and the generator unit 10.

As shown in FIG. 9A, the generator unit 10 is mounted to the case 2 in such a way that the shroud 38 surrounding the engine 20 and bolted to opposite sides of the engine 20 is attached to the reinforced mounting portion 4a of the carrying handle 4, and the base 11 carrying thereon the engine 20 and bolted to the engine 20 is attached to the bottom portion 2B of the case 2 which has a relatively high stiffness.

As shown in FIG. 9B, a top portion 2H of the case 2 (including the carrying handle 4 and the reinforced mounting portions 4a, 4a of the handle 4), which is indicated by phantom-lined hatching, is made to have a higher stiffness than other portions because this portion 2H must sustain the weight of components, such as the shroud 38, the generator unit 10 and the like, hanging from the same portion 2H. Similarly, the bottom portion 2B (FIG. 9A) of the case 2 is made stiffer than other portions because it is subjected to the weight of components contained in the case 2.

As shown in FIG. 9C, when the user is carrying the portable generator 1 from one place to another with the carrying handle 4 gripped with its hand H, the weight of the generator unit 10 including the engine 20 mostly acts through the shroud 38 on the reinforced mounting portion 4a and thence on the carrying handle 4. The shroud 38 has a high stiffness and serves also as a support member (hanger) for supporting or hanging the engine 20 from the reinforced mounting portion 4a. With this mounting structure, a side portion 2S of the case 2 is not so requested to bear the weight of the generator unit 10.

As is apparent from the foregoing description, when the portable generator 1 is being hand-carried by the user, most of the weight of the generator unit 10 including the engine 20 acts on the top and bottom portions 2H, 2B of the case 2. Taking this into consideration, the side portion 2S of the case 2 may be constructed to have only a small stiffness. There is no need to increase the stiffness throughout the whole body of the case 2, and so considerable weight reductions of the case 2 become possible. Additionally, the portable generator 1 of the present invention, as opposed to the conventional apparatus, requires no frames to hold the case 2 and, hence, is free from limitations resulting from the presence of the frames. Thus, the case 2 has a high degree of flexibility not only in terms of the geometric design but also in terms of the selection of materials used.

Additionally, because at least the crankcase 21 and the cylinder block 22 of the engine 20 are covered or shrouded doubly by the shroud 38 and the case 2, an enhanced sound-insulating effect can be obtained.

Furthermore, since the shroud 38 doubles in function as a shroud for cooling and ventilating the engine 20 and also as a support member (hanger) of the engine 20, the internal structure of the portable generator 1 can be simplified.

Referring now to FIG. 10, there is shown the control unit accommodating box 72 and the fuel tank 74 stably held in position within the case 2.

As shown in FIG. 10, a pair of right and left lower cushion members 71R, 71L is disposed on a bottom surface 2a of the case 2 for supporting thereon the control unit accommodating box 72. An intermediate cushion member 73 (composed of a right piece 73R and a left piece 73L separated from each other) is associated with upper right and left corner portions of the control unit accommodating box 72. The intermediate cushion member 73 supports thereon the fuel tank 74. The fuel tank 74 has a tubular fuel filler port 74a formed at its upper end and projecting upwardly and outwardly from an upper portion of the case 2.

The control unit accommodating box 72 is a relatively stiff rectangular box and accommodates within it a control unit (not shown) for controlling the engine 20 and generator body 33 shown in FIG. 2. The control unit accommodating box 72 (hereinafter referred to as "accommodating box") has a pair of right and left legs 72a, 72a at the bottom and a positioning lateral projection 72b at an upper right corner. The right and left legs 72a, 72a are mounted on the bottom surface 2a of the case 2 via the lower cushion members 71R, 71L. More specifically, the legs 72a, 72a carrying thereon the lower cushion members 71R, 71L are fitted in a pair of aligned guide grooves 2b, 2b formed transversely in the bottom surface 2a of the case 2. The legs 72a, 72a and the lower cushion members 71R, 71L are movable along the guide grooves 2b, 2b so that the position of the accommodating box 72 relative to the case 2 can be adjusted in the transverse direction of the case 2.

The fuel tank 74 further has a pair of positioning projections 74b formed integrally with and projecting horizontally from lower right and left corners of the fuel tank 74. An annular upper cushion member 75 is fitted around a root or base portion of the fuel filler port 74a. A filler cap 76 is attached to an upper end of the fuel filler port 74a to close the fuel filler port 74a.

The case 2 has an upper hole 2c formed at mating surfaces of the right and left case members 2R, 2L. The upper cushion member 75 is also fitted in the upper hole 2c so that the fuel filler port 74a is supported by an inner edge of the upper hole 2c with the upper cushion member 75 disposed therebetween.

The right piece 73R of the intermediate cushion member 73 is attached by press-fitting to a portion of the inner surface of a sidewall of the right case member 2R. Similarly, the left piece 73L of the intermediate cushion member 73 is attached by press-fitting to a portion of the inner surface of a sidewall of the left case member 2L. A joint structure between the right and left intermediate cushion member pieces 73R, 73L and the right and left case members 2R, 2L will be described below.

The right and left intermediate cushion member pieces 73R, 73L have a generally T shape including a vertical base portion 73a and a horizontal wing portion 73b. These pieces 73R, 73L are arranged such that the respective wing portions 73b, 73b confront each other in a horizontal plane.

The opposed horizontal wing portions 73b, 73b are disposed between an upper surface of the accommodating box 72 and a lower surface of the fuel tank 74. A total weight of the accommodating box 72 and fuel tank 74 is applied via the lower cushion members 71R, 71L and the horizontal wing portions 73b, 73b to the bottom portion 2B (FIG. 8) of case 2 which is made stiffer than other portions.

The vertical base portion 73a of the right intermediate cushion member piece 73R has formed therein an upper recessed portion 73C for positioning the fuel tank 74, and a lower recessed portion 73d for positioning the accommodating box 72. The left intermediate cushion member piece 73L has a recessed portion 73c formed in the vertical base portion 73a for positioning the fuel tank 74.

The base portion 73a of the left intermediate cushion member piece 73L is held in direct contact with a left side surface of the accommodating box 72, and the lower recessed portion 73d of the right intermediate cushion member piece 73R is fitted with the positioning projection 72b of the accommodating box 72 so that the right and left case members 2R, 2L can stably hold the accommodating box 72 in position by gripping the accommodating box 72 at the upper right and left corners via the right and left intermediate cushing member pieces 73R, 73L.

Similarly, the recessed portions 73c, 73c of the right and left intermediate cushion member pieces 73R, 73L are fitted with the right and left positioning projections 74b, 74b of the fuel tank 74 so that the right and left case members 2R, 2L can stably hold the fuel tank 74 in position by gripping the fuel tank 74 at the lower right and left corners via the right and left intermediate cushing member pieces 73R, 73L.

The lower cushion members 71R, 71L (71), intermediate cushion member 73 (73R, 73L) and upper cushion member 74 are made from an elastic material such as rubber.

As appears clear from the foregoing description, the accommodating box 72 holding therein the control unit (not shown) is carried via the lower cushion members 71R, 71L on the bottom portion 2B (FIG. 8) of case 2 which is made stiffer than other portions of the case 2, and fuel tank 74 is mounted on the accommodating box 72 via the intermediate cushion member 73. By using such simple two-storied arrangement, the fuel tank 72 (which becomes heavy when filled) can be readily accommodated within an upper part of the case 2. Additionally, the fuel filler port 74a projecting from an upper portion of the case 2 insures easy filling of the fuel to the fuel tank 74 accommodated within the case 2.

The weight of the fuel tank 71 is applied to the bottom surface 2a of the bottom portion 2B (FIG. 8) through the intermediate cushion member 73, the relatively stiff accommodating box 72 and the lower cushion member 71. Since the weight of the fuel tank 74 is born by the relatively stiff accommodating box 72, and since vibrations and shocks are damped by the lower and intermediate cushion members 71, 73, there is no strong need to increase the stiffness of the whole body of the case 2. Instead, partial stiffening of the case 2, as done at the top and bottom portions 2H and 2B (FIG. 9A), is satisfactory, which enables considerable reductions in weight of the case 2 and provides a higher degree of flexibility in designing the geometric shape of the case 2 and selecting materials used for the case 2, as compared to the conventional structural means taken to increase the stiffness of the case.

The right and left cover members 2R, 2L concurrently grip the opposite sidewalls of the accommodating box 72 and opposite sidewalls of the fuel tank 74 through the right and left intermediate cushion member pieces 73R, 73L, so that the accommodating box 72 and the fuel tank 74 are stably held in position within the case 2. Since the accommodating box 72 and the fuel tank 74 are automatically brought to a final attachment position when they are gripped as just described above, an attachment structure of the accommodating box 72 and fuel box 74 relative to the case 2 is very simple in construction. Furthermore, horizontal vibrations and shocks tending to act on the accommodating box 72 and the fuel tank 74 are sufficiently damped by the right and left intermediate cushion member pieces 73R, 73L.

At the upper hole 2c of the case 2, the fuel filler port 74a of the fuel tank 74 is gripped by the right and left case member 2R, 2L with the upper cushion member 75 disposed between the fuel filler port 74a and the inner edge of the upper hole 2c. Thus, the fuel tank 74 is stably and reliably attached to the case 2.

Referring now to FIG. 11, there is shown in exploded perspective a joint structure used for attaching the right intermediate cushion member 73R to the right cover member 2R shown in FIG. 10.

The right cover member 2R includes pair of spaced retaining projections 2d, 2d, projecting perpendicularly from an inside surface of the cover member 2R. The retaining projections 2d, 2d, are tapered and each have four radial wings arranged in the shape of a cross like a tip of a Phillips driver.

The right intermediate cushion member piece 73R has a pair of spaced locking recesses 73e, 73e adapted to be press-fitted with the retaining projections 2d, 2d. To this end, the locking recesses 73e, 73e are complementary in contour to the retaining projections 2d, 2d. The locking recesses 73e, 73e and the retaining projections 2d, 2d, are press-fitted with each other to attach the right intermediate cushion member piece 73R to the right case member 2R.

The right intermediate cushion member piece 73R has a pair of parallel spaced ribs 73f formed integrally with an upper surface of the horizontal wing portion 73b. The ribs 73f are triangular in cross section and has a ridge of an acute angle. The ribs 73f support thereon a lower surface of the fuel tank 74 and they are elastically deformable to an extent proportional to the quantity of fuel held in the fuel tank 74.

A joint structure used for attaching the left intermediate cushion member 73L (FIG. 10) to the left cover member 2L (FIG. 10) is the same as the joint structure just described above with reference to FIG. 11, and a further description thereof can be omitted.

A sequence of processing steps taken to assemble the portable generator 1 of the foregoing construction will be described with reference to FIG. 12. The processing steps should be construed as illustrative and not restrictive.

At first, the right case member 2R having a inner inner control panel 82 screwed thereto in advance is set in an assembling site with the inside surface of the sidewall (or the mating surface) facing upwards. The right intermediate cushion member piece 73R is also attached in advance to the right cover member 2R.

Then, the generator unit 10 while kept in a half-rolled position above the right cover member 2R is placed down onto the right cover member 2R so that the right first leg 54a and the right second legs 64a, 64a of the generator unit 10 are fitted in the socket portions 4b, 4c, 4c of the right case member 2R.

Subsequently, the lower cushion members 71R, 71L are fitted over the legs 72a, 72a of the accommodating box 72.

Thereafter, the accommodating box 72 while kept in a half-rolled position above the right cover member 2R is placed down onto the right cover member 2R such that the right lower cushion member 71R is fitted into the positioning groove 2b of the right case member 2R, and the positioning projection 72b of the accommodating box 72 is fitted in the recessed portion 73d of the right intermediate cushion member piece 73R.

Then, the fuel tank 74 while kept in a half-rolled position above the right cover member 2R is placed down onto the right cover member 2R such that the positioning projection 74b of the fuel tank 74 is fitted in the recessed portion 73c of the right intermediate cushion member piece 73R.

Subsequently, the left cover member 2L having the left intermediate cushion member piece 73L attached thereto in advance is placed down onto the right cover member 2R while the inside surface of the sidewall (or the mating surface) of the left cover member 2L facing downwards.

Thereafter, the left cover member 2L is mated with the right cover member 2R such that the left first leg 54a and the left second legs 64a, 64a of the generator unit 10 are fitted into the socket portions 4b, 4c, 4c of the left cover member 2L. During that time, the positioning groove 2b of the left cover member 2L fittingly receives therein the left lower cushion member 71L, and the left intermediate cushion member piece 73L is brought into abutment with the left sidewall of the accommodating box 72. In this instance, the recessed portion 73c of the left intermediate cushion member piece 73L is fitted with the positioning projection 74b of the fuel tank 74.

Then, the left and right case members 2L, 2R assembled together in superposed relation are fastened together by means of the screws B9, B9, B11, B11. The inner control panel 82 is firmly secured by a screw (not shown) to the left cover member 2L.

Subsequently, seal members 81 and the control panel 5 are placed over the inner control pane 82 through a front opening of the cover 2, and the control panel 5 is secured by a screw B13 to the inner control panel 82 with the seal members 81 disposed between the two panels 5, 82.

Then, seal members 43 are fitted on the exhaust duct 44 and after that the exhaust duct 44 is inserted into the exhaust hole 45 until it is fitted with the outlet 38b of the shroud 38 with the seal members 43 disposed therebetween. The exhaust duct 44 is secured by screws B14 (one being shown) to the case 2. A portable generator 1 of the present invention is thus completed.

As will be understood from the foregoing description, the portable generator 1 can be built up by merely assembling together the right case member 2R, the generator unit 10, the accommodating box 72, the fuel tank 74 and the left case member 2L from one direction in the order described above. Such unidirectional assembling operations do not involve frequent changes in position and posture of the components which are tedious and time-consuming. Accordingly, the efficiency of the assembling process is veery high.

Additionally, by virtue of the fitting engagement between the legs 54a, 64a, 64a of the generator unit 10 and the socket portions 4b, 4c, 4c of the right and left case members 2R, 2L, the right and left case members 2R, 2L and the generator unit 10 are temporarily assembled together with the generator unit 10 stably held therebetween. The number of portions to be joined together by screws can, therefore, be reduced and the assembling efficiency increases further.

A cooling system of the portable generator 1 will be described with reference to FIG. 13.

When the engine 20 of the generator unit 10 is started, the generator body 33 begins to generate electric power. This causes the cooling fan 34 to rotate in unison with the outer rotor 33c of the generator body 33.

Rotation of the cooling fan 34 causes outside air to be drawn from the air inlets 6 into the case 2 and thence into the fan cover 37 through the air inlet 37a. The outside air is then forced or driven by the rotating cooling fan 37 to flow downstream through the fan cover 37, the shroud 38 and exhaust duct 44 to successively cool the generator body 33, the engine 20, the exhaust pipe 31 and the muffler 32. After cooling of the components 33, 20, 31, 32, the outside air is exhausted from the vent holes 44a (exhaust hole 45) of the exhaust duct 44.

The fan cover 35, shroud 38 and exhaust duct 44 connected end to end to form a single cooling passage. The cooling fan 34 is disposed in the cooling passage so that the outside air is drawn from the inlet 6, successively cools the generator body 33, engine 20, exhaust pipe 31 and muffler 32, and is finally exhausted from the exhaust hole 45 (vent holes 44a).

The cooling system composed of a single cooling passage (formed by an in-line arrangement of the fan cover 34, shroud 38 and exhaust duct 44) and a single cooling fan 34 occupies only a small space within the case 2 and hence enables downsizing of the portable generator 1.

A noise source formed by the generator body 33 and the cooling fan 34 associated therewith is enclosed in the fan cover 37. Another noise source formed by the engine 20 is enclosed in the shroud 38. The fan cover 37 containing the first noise source and the shroud 38 containing the second noise source are received in the case 2. Thus, the noise sources are doubly sound-insulated. With this double sound-insulating structure, the noise-proofing properties of the portable generator 1 are very high.

Description given below is directed to the cooling capacity or power of the engine 20.

The shroud 38 made of metal (steel plate in the illustrated embodiment) is directly attached to the engine 20, as shown in FIG. 5. Heat of an outer wall of the engine 20 is, therefore, directly transferred to the metal shroud 38. The metal shroud 38 directly attached to the engine 20 forms an effective radiating element and gives an additional heat-radiating surface to the engine 20. The engine 20 having such additional heat-radiating surface possesses a large cooling capacity or power and, hence, can be sufficiently cooled even when the cooling fan 34 is relatively small. Additionally, the use of the metal shroud 38 is contributive to the downsizing of the portable generator 1.

FIG. 14 shows a modified form of the case 2 according to the present invention. The modified case, which is also designated by 2, differs from the case 2 shown in FIGS. 1-13 only in that it includes a carrying handle 4 provided below an upper surface of the case 2 as a part of a body of the case 2. In this embodiment, the shroud 38 is attached to an upper case portion 2H (including the carrying handle 4 and the reinforced mounting portion 4a of the carrying handle 4) indicated by phantom-lined hatching for clarity. With this arrangement, the weight of the shroud 38 can be effectively supported even when the carrying handle 4 does not project from the upper surface of the case 2.

The metal shroud 38 which is directly attached to the case 2 to increase heat-radiating capacity or power of the engine 20 is preferably formed from a material having a large thermal conductivity (heat-transfer coefficient), such as a steel sheet or an aluminum plate. A steel plate having a large stiffness is much preferable from a load-bearing point of view because the engine 20 accommodated within the shroud 38 is heavy. The shroud 38 may be attached to a body of the carrying handle 4 rather than to the root (reinforced mounting portion) 4a of the handle 4.

Furthermore, the socket portions 4b, 4c, 4c of the case 2 and the legs 54a, 64a, 64a of the generator unit 10 may take another form as long as they can fit with each other. Additionally, the right lower cushion member 71R and the left lower cushion member 71L may be integral with each other.

Obviously, various minor changes and modifications of the present invention are possible in the light of the above teaching. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.