Background Art Generally, a twin pump had been developed in such a way as to perform a function of a rotary pump for force-feeding fluid such as liquid having a high viscosity, or the like, and at the same time of a vacuum pump for force-feeding air, gas or the like.

Hereinbelow, a twin pump disclosed in Korean Patent Publication No. 97-9955 which was filed in the name of the present applicant, will be described as a typical example of twin pumps.

In other words, FIG. 1 is a cross-sectional view illustrating a construction of a conventional twin pump including a pair of cylinders and a piston. The conventional twin pump includes a casing 100. The casing 100 has an inlet port 101 and an outlet port 102 which are defined on lower and upper surfaces, respectively, of the casing 100. A pair of circular cylinders 103 are defined in the casing 100 in a manner such that they are communicated with each other. In the pair of circular

cylinders 103, there is disposed a piston 200. The piston 200 is formed, at both ends thereof, with a pair of head sections 201 which are connected with each other by a linear plate section 202 and are respectively located in the pair of circular cylinders 103.

The head sections 201 which are formed at both ends of the piston 200, are mounted, at center portions thereof, to eccentric cams 301, respectively, which are rotated in opposite directions from each other via camshafts 300 by driving means.

Therefore, if the camshafts 300 are driven by the medium of gears in the opposite directions from each other by the driving means, the eccentric cams 301 which are mounted to the center portions of the pair of head sections 201 constituting the piston 200, are also rotated in the opposite directions from each other.

Hence, the head sections 201 are symmetrically moved in the circular cylinders 103 along opposite loci from each other, respectively, in a manner such that circumferential outer surfaces of the head sections 201 are brought into close contact with circumferential inner surfaces of the circular cylinders, respectively.

As a consequence, the twin pump allows fluid or gas to be repeatedly intaken through the inlet port 101 into the casing 100 and then to be force-fed toward the outlet port 102 of the casing 100.

However, the conventional twin pump constructed as mentioned above suffers from defects in that, as shown in FIG. 1, immediately before one head section 201 which is formed at one end of the piston 200, is brought into close contact with the circumferential inner surface of

one cylinder 103, that is, immediately before one eccentric cam 301 which is mounted at the center portion of the one head section 201, reaches a top dead center, due to a momentary closing phenomenon for fluid or gas, fluid or gas which is present in the other cylinder 103, is excessively pressed.

Therefore, at this time, a gap G is created between the circumferential outer surface of the other head section 201 of the piston 200 and the circumferential inner surface of the other cylinder 103, and backflow of the fluid which is present in the outlet port 102, toward the inlet port 101, occurs. For this reason, it is difficult for the conventional twin pump to serve as a high pressure pump.

On the other hand, in order to prevent the gap G from being created, as shown in FIG. 2, projections 400 are formed on the circumferential outer surfaces of the pair of head sections 201 which are formed at both ends of the piston 200. However, in this case, it is difficult to prevent, in a sufficient manner, the piston 200 from being detached from the circumferential inner surface of the cylinder 103 due to the momentary closing phenomenon. Consequently, the conventional twin pump as shown in FIG. 2, is encountered with a problem in that the backflow of the fluid which is present in the outlet port 102, toward the inlet port 101, still occurs.

Also, due to the fact that the projections 400 are excessively pressed while the piston 200 is operated, power consumption is increased and output efficiency is degraded. Moreover, as friction of the projections 400 is maximized, lifetime of the twin pump is shortened.

Disclosure of the Invention Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a twin pump which always reliably isolates an intaking part and a discharging part from each other while a piston disposed in a cylinder is operated, thereby preventing backflow of pressure medium.

Another object of the present invention is to provide a twin pump wherein a pair of head sections which are respectively formed at both ends of a piston, are connected with each other by virtue of an intermediate connecting section which is defined at upper and lower surfaces thereof with a pair of recessed portions, respectively, whereby it is possible to enhance pump capacity without increasing a volume of the pump.

In order to achieve the above objects, according to one aspect of the present invention, there is provided a twin pump comprising: a casing having an inlet port and an outlet port which are defined at center portions of lower and upper surfaces thereof, the casing further having a pair of cylinders which are defined in a manner such that they are communicated with each other; a piston disposed in the pair of cylinders and formed, at both ends thereof, with a pair of head sections which are symmetrized with each other, each head section being formed, at an inner end and at each of upper and lower regions, with a close-contact section having a rounded convex portion and a rounded concave

portion which are consecutively connected with each other, a circumferential inner surface of each of the pair of cylinders being formed in a manner such that a circumferential outer surface of each of the pair of head sections can be brought into close contact therewith while being moved thereon, the casing being formed, between the pair of cylinders and the inlet port and the outlet port, with semi-circular seating parts so that close-contact sections of the piston can be brought into close contact with the semi-circular seating parts; and a pair of eccentric cams fitted through center portions of the pair of head sections and rotated in directions opposite to each other via camshafts by means of driving means, a distance between centers of the camshafts being equal to a distance between centers of the eccentric cams which are fitted through the head sections of the piston.

According to another aspect of the present invention, the circumferential inner surfaces of the pair of cylinders are formed to each have a U-shaped contour so that the circumferential inner surfaces are symmetrized with each other; and the circumferential outer surfaces of the pair of head sections which are formed at both ends of the piston, are formed to each have a U-shaped contour so that the circumferential outer surfaces are symmetrized with each other.

According to still another aspect of the present invention, in the case that the pair of head sections of the piston are moved via the camshafts in the directions opposite to each other, the head sections which are formed at both ends of the piston and the close-contact

sections are brought into close contact with the circumferential inner surfaces of the cylinders and inner surfaces of the semi-circular seating parts, simultaneously at two or more places.

According to yet still another aspect of the present invention, the pair of head sections which are formed at both ends of the piston, are connected with each other by virtue of an intermediate connecting section, the intermediate connecting section being formed, at upper and lower surfaces thereof, with a pair of circularly recessed portions which are recessed inward in a manner such that an intaking volume and a discharging volume can be increased.

Brief Description of the Drawings The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description when taken in conjunction with the drawings, in which: FIG. 1 is a cross-sectional view illustrating a construction of a conventional twin pump including a pair of cylinders and a piston; FIG. 2 is a cross-sectional view illustrating a construction of another conventional twin pump including a pair of cylinders and a piston; FIG. 3 is a cross-sectional view illustrating a construction of a twin pump including a pair of cylinders and a piston, in accordance with an embodiment of the present invention; and FIGs. 4a through 4d are cross-sectional views

illustrating operations of the twin pump according to the present invention, wherein FIG. 4a shows an initial operating status, FIGs. 4b and 4d show intermediate operating statuses and FIG. 4c shows a final operating status.

Best Mode for Carrying Out the Invention Reference will now be made in greater detail to a preferred. embodiment of the invention, an example of which is illustrated in the accompanying drawings.

Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.

FIG. 3 is a cross-sectional view illustrating a construction of a twin pump including a pair of cylinders and a piston, in accordance with an embodiment of the present invention. The twin pump according to the present invention includes a casing 1. The casing 1 has an inlet port 11 and an outlet port 12 which are defined at center portions of lower and upper surfaces of the casing 1. The casing 1 further has a pair of cylinders 13 which are defined in a manner such that they are communicated with each other. A piston 2 is disposed in the pair of cylinders 13. The piston 2 is formed, at both ends thereof, with a pair of head sections 21 which are symmetrized with each other. Each head section 21 is formed, at an inner end and at each of upper and lower regions thereof, with a close-contact section 23. Each close contact section 23 has a rounded convex portion 231 and a rounded concave portion 232 which are continuously connected with each other. A

circumferential inner surface of each of the pair of cylinders 13 is formed in a manner such that a circumferential outer surface of each of the pair of head sections 21 can be brought into close contact therewith while being moved thereon. The casing 1 is formed, between the pair of cylinders 13 and the inlet port 11 and the outlet port 12, with semi-circular seating parts 132 so that close-contact sections 23 of the piston 2 can be brought into close contact with the semi-circular seating parts 132. A pair of eccentric cams 31 are fitted through center portions of the pair of head sections 21 and rotated in directions opposite to each other via camshafts 3 by means of driving means.

At this time, a distance Ll between centers a of the camshafts 3 equals to a distance L2 between centers b of the eccentric cams 31 which are fitted through the head sections 21 of the piston 2.

Hence, in the case that the eccentric cams 31 are rotated in the directions opposite to each other by means of the driving means (not shown), due to the fact that the distance Ll between the centers a of the camshafts 3 equals to the distance L2 between the centers b of the eccentric cams 31, the pair of head section 21 which are formed at both ends of the piston 2, can be symmetrically moved along predetermined loci, respectively.

Therefore, as shown in FIGs. 4b and 4d, in the case that the pair of head sections 21 of the piston 2 are moved via the camshafts 3 in the directions opposite to each other, the head sections 21 which are formed at both ends of the piston 2 and the close-contact sections

23 are brought into close contact with the circumferential inner surfaces of the cylinders 13 and inner surfaces of the semi-circular seating parts 132, simultaneously at two or more places. By this, the inlet port 11 and the outlet port 12 can always be isolated from each other.

On the other hand, the circumferential inner surfaces of the pair of cylinders 13 are formed to each have a U-shaped contour so that the circumferential inner surfaces are symmetrized with each other. And, the circumferential outer surfaces of the pair of head sections 21 which are formed at both ends of the piston 2, are formed to each have a U-shaped contour so that the circumferential outer surfaces are symmetrized with each other. By this, the piston 2 can be smoothly moved in the pair of cylinders 13.

In particular, as shown in FIG. 3, a distance dl between a middle of the circumferential inner surface of one cylinder 13 and the semi-circular seating parts 132 formed in inner upper and lower portions of the other cylinder 13, is formed in such a way as to be relatively longer than a distance d2 between a middle of the circumferential outer surface of one head section 21 which is formed at one end of the piston 2 and a free end of the close-contact section 23 which is formed at the inner end of the other head section 21.

As a consequence, even in the case that the eccentric cams 31 are rotated toward their top dead centers, as shown in FIGs. 4a and 4c, the piston 2 is held horizontal. Further, since outer surfaces of the close-contact sections 23 which are positioned at the

inner ends of the pair of head sections 21 of the piston 2, are brought into close contact with inner surfaces of the semi-circular seating parts 132 of the pair of cylinders 13, it is possible to prevent backflow of fluid or air which is present in the outlet port 12, toward the inlet port 11.

The pair of head sections 21 which are formed at both ends of the piston 2, are connected with each other by virtue of an intermediate connecting section 22. The intermediate connecting section 22 is formed, at upper and lower surfaces thereof, with a pair of circularly recessed portions 221 which are recessed inward in a manner such that an intaking volume and a discharging volume can be increased. By this, without increasing a volume of the twin pump, pump capacity can be enhanced.

Industrial Applicability As a result, by the twin pump according to the present invention, advantages are provided in that, since an intaking part and a discharging part are always isolated from each other in a reliable manner while a piston disposed in a cylinder is operated, backflow of pressure medium is prevented, whereby the twin pump can serve as a high output (high pressure) pump.

Moreover, because pump capacity can be enhanced without increasing a volume of the pump, it is possible to obtain an efficiency of a high capacity pump with a reduced volume.