Sea Water Cooling Apparatus for Marine Diesel Engine

The present invention relates to a sea water cooling apparatus for a marine diesel engine with a supercharger.

Hitherto, a sea water cooling apparatus for a marine diesel engine with a supercharger for use in a power boat or the like has been structured as shown in FIGS. 9 or 10. A sea water pump 4 has, on the inlet side thereof, an inlet conduit 6 the opening of which is positioned below the sea level 11 and, on the outlet side thereof, it has outlet conduits 7a and 7b through which cooling sea water passes and in which an after cooler 3 for the supercharger, an oil cooler 2 for the engine and an engine 1 are disposed. A thermostat 5 is disposed between the outlet conduits 7a and 7b, the thermostat 5 and the inlet conduit 6 of the sea water pump 4 being connected to each other by a bypass conduit 8. A fuel injection pump (omitted from illustration) is provided with an overflow valve for equalizing the temperature and the pressure of the fuel in such a manner that it is connected to a fuel tank 13 by an overflow conduit 15. When the engine 1 is operated under light load and thereby shows low temperature, the thermostat 5 is completely closed and cooling sea water supplied from the sea water pump 4 is warmed up by the engine 1 before it circulates the outlet conduit 7a, the thermostat 5 and the bypass conduit 8 so that the warming up operation is performed. When the load of the engine 1 is enlarged and thereby the temperature of cooling sea water is raised to a predetermined level, the thermostat 5 is completely opened so that cooling sea water cools the after cooler 3 for the supercharger, the oil cooler 2 for the engine and the engine 1 before it is discharged to the sea level 11 via the outlet conduit 7a, the thermostat 5 and the outlet conduit 7b.

However, in the sea water cooling apparatus for a marine diesel engine with a supercharger constituted in such a manner that the after cooler 3, the oil cooler 2 and the engine 1 are disposed in series, a problem arises in that a satisfactory large output cannot be obtained because the temperature of air at the outlet port of the after cooler is undesirably raised by the thermostat in a case where a rapid acceleration operation is performed after the warming-up operation has been performed or in a case of an operation under large load.

Another problem arises in that the temperature of fuel in the fuel tank is undesirably raised by fuel returned from the overflow valve, and, in particular, that the output is undesirably reduced if the quantity of fuel in the fuel tank is reduced.

An object of the present invention is to overcome the above-described conventional problems by providing a sea water cooling apparatus for a marine diesel engine which is arranged in such a manner that an opening/closing valve device is disposed in the bypass conduit, with which a satisfactory large output can be obtained even if a rapid accelerating operation is performed after the warming up operation has been performed or in a case of an operation under large load and in which fuel can be effectively cooled by a fuel cooler.

A first aspect of the present invention lies in a sea water cooling apparatus for a marine diesel engine with a supercharger arranged in such a manner that an after cooler, an oil cooler and an engine are disposed on the outlet side of a sea water pump, a thermostat is disposed in an outlet conduit for cooling sea water disposed next to the sea water pump and the thermostat and an inlet conduit of the sea water pump are connected to each other by a bypass conduit, the sea water cooling apparatus comprising: a second bypass conduit for establishing a connection between the upstream side of the thermostat and the downstream side of the thermostat and an opening/closing valve device inserted into the second bypass conduit.

Therefore, the degree of opening of the opening/closing valve device can be controlled and the undesirable rise in the temperature of the air at the outlet port of the after cooler by the thermostat can be prevented even if a rapid accelerating operation is performed after the warming up operation has been performed or in a case of an operation under large load.

A second aspect of the present invention lies in an additional arrangement to the above-described aspect in which a fuel cooler is disposed in the outlet conduit for cooling sea water at a position between the sea water pump and the thermostat; and the fuel cooler, the engine and a fuel tank provided for the engine are connected to one another by a fuel conduit.

As a result of the above-described structure, fuel can effectively be cooled.

The opening/closing valve device comprises: a plunger having a plurality of small apertures; and a cylinder including a spring and arranged in such a manner that the plunger is completely opened when the discharge pressure from the sea water pump exceeds the setting pressure for the spring. Another structure may be employed in which it comprises: a cylinder including a butterfly type opening/closing valve; a cylinder having a suction port for the discharge pressure from the supercharger and including a piston rod and a spring; and a link for establishing a connection between the opening/closing valve and the piston rod and which is arranged in such a manner that the opening/closing valve is completely opened when the discharge pressure from the supercharger exceeds the setting pressure of the spring. The opening/closing valve device may comprise: a cylinder including a butterfly type opening/closing valve, a rod, an end portion of which is rotatably connected to the shaft of the opening/closing valve and another end portion of which has a solenoid; and a controller for controlling the operation of the solenoid by detecting the discharge pressure from the supercharger and the engine revolution speed and arranged in such a manner that the opening/closing valve is completely opened when the discharge pressure from the supercharger and the engine revolution speed respectively exceed predetermined values.

FIG. 1 is a circuit diagram which illustrates a first mode of a sea water cooling apparatus according to the present invention;

FIG. 2 is a circuit diagram which illustrates a second mode of the sea water cooling apparatus according to the present invention;

FIG. 3 is an enlarged view which illustrates an opening/closing valve device according to the present invention;

FIG. 4 is a graph which illustrates the relationship between the engine revolution speed and the discharge pressure from the sea water pump;

FIG. 5 is an enlarged view which illustrates an applicable example of the opening/closing valve device shown in FIG. 3;

FIG. 6 is a graph which illustrates the relationship between the engine output and the discharge pressure from the supercharger;

FIG. 7 is an enlarged view which illustrates another applicable example of the opening/closing valve device shown in FIG. 3;

FIG. 8 illustrates the relationship between the engine revolution speed and the discharge pressure from the supercharger; and

FIGS. 9 and 10 are circuit diagrams for use in a conventional sea water cooling apparatus.

The structure of a first mode of the present invention will now be described with reference to FIG. 1. Referring to FIG. 1, the same elements as those according to the conventional structure are given the same reference numerals. A sea water pump 4 has, on the inlet side thereof, an inlet conduit 6 the opening of which is positioned below the sea level 11 and, on the outlet side thereof, it has outlet conduits 7a and 7b through which cooling sea water passes and in which an after cooler 3 for the supercharger, an oil cooler 2 for the engine and an engine 1 are disposed. A thermostat 5 is disposed between the outlet conduits 7a and 7b, the thermostat 5 and the inlet conduit 6 of the sea water pump 4 being connected to each other by a bypass conduit 8. A second bypass conduit 10 having an opening/closing valve device 90, which is controlled by the load of the engine 1, is disposed in parallel to the outlet conduits 7a and 7b in such a manner that it bypasses the thermostat 5. The engine 1 performs the low load operation.

When the engine 1 is accelerated and its load is thereby enlarged, the opening/closing valve device 90 is opened. In accordance with the rise in the temperature of cooling sea water, the thermostat 5 is also opened so that cooling sea water introduced from the outlet conduit 7a is branched into flows which are respectively introduced into the opening/closing valve unit 90 and the thermostat 5 in such a manner that a portion of sea water is then discharged to the sea level 11 after two flows have again joined together in the outlet conduit 7b and another portion of it is then circulated to the inlet portion of the sea water pump 4 through the first bypass conduit 8.

When the load of the engine 1 is enlarged to a predetermined level and also the temperature of cooling sea water is raised to a predetermined level, the opening/closing valve device 90 and the thermostat 5 are completely opened, causing the overall quantity of cooling sea water introduced from the outlet conduit 7a to join together in the outlet conduit 7b before it is discharged to the sea level 11.

As described above, according to this mode, cooling sea water can be controlled in accordance with the temperature and the load of the engine.

The structure of a second mode of the present invention will now be described with reference to FIG. 2. Referring to FIG. 2, the same elements as those shown in FIG. 1 are given the same reference numerals and their descriptions are omitted here. On the outlet port side of the sea water pump 4, a fuel cooler 12 is inserted. The fuel cooler 12 has a fuel inlet conduit 14a connected to the fuel tank 13 and an outlet conduit 14b connected to the engine 1. A fuel injection pump (omitted from illustration) of the engine 1 is provided with an overflow valve for equalizing the temperature and pressure of fuel. The above-described valve and the fuel tank 13 are connected to each other by the overflow conduit 15. Although the temperature in the fuel tank 13 is raised by fuel returned from the overflow conduit 15, it can be effectively cooled by the above-described fuel cooler 12.

The remaining operations are performed similarly to those according to the first mode and thereby their descriptions are omitted here.

According to this mode, fuel can be effectively cooled by a simple structure in addition to the effect obtainable from the above-described first mode.

FIG. 3 is an enlarged view which illustrates an opening/closing valve device 91 which is operated in accordance with the discharge pressure from the sea water pump 4 according to the present invention. Referring to the drawing, a cylinder 91a having a seating surface 91b and water chambers 91c and 91d is disposed in parallel to the outlet conduits 7a and 7b, the cylinder 91a being disposed in the second bypass conduit 10 which is continuously formed to bypass the thermostat 5. A plunger 91e of a hollow type and having a plurality of small apertures 91f is included in the cylinder 91a in such a manner that it is brought into close contact with the seating surface 91b by a spring 91g. FIG. 4 is a graph which illustrates the relationship between engine revolution speed N and sea water pump discharge pressure Hp. The set pressure for the spring 91g is made to be the same as discharge pressure Hp.sub.1 from the sea water pump When the engine revolution speed is, as shown in FIG. 3, N.sub.1.

As a result of the above-described setting, cooling sea water introduced from the outlet conduit 7a passes through the second bypass conduit 10 to completely open the plunger 91e so as to be discharged to the sea level 11 through the outlet conduit 7b from a plurality of the small apertures 91f when the discharge pressure from the sea water pump exceeds Hp.sub.1. Since the operation of the thermostat 5 is performed similarly to that shown in FIG. 1, its description is omitted here.

FIG. 5 is an enlarged view which illustrates an opening/closing valve device 92 which is operated in accordance with the discharge pressure from the supercharger, wherein an example of an application of the structure shown in FIG. 3 is shown. A cylinder 92a including a butterfly type opening/closing valve 92b is disposed in parallel to the outlet conduits 7a and 7b, the cylinder 92a being disposed in the second bypass conduit 10 which is continuously formed to bypass the thermostat 5. A shaft 92c is an attachment shaft for attaching the opening/closing valve 92b, the shaft 92c being connected to a link 92k having an elongated hole 92j. A piston 92f of an actuator is, via a spring 92h, fastened to a cylinder 92d which opens in a discharge pressure suction port 92e of the supercharger. A rod 92g is integrally formed with the piston 92f in such a manner that it is, by a pin 92l, slidably connected to an elongated hole 92j formed in a link 92k. FIG. 6 is a graph which illustrates the relationship between engine output P and supercharger discharge pressure Ht. The setting pressure for the spring 92h is made to be the same as discharge pressure Ht.sub.1 from the supercharger when the engine output is P.sub.1. As a result of the above-described setting, the discharge pressure from the supercharger supplied through the suction port 92e acts on the piston 92f and the rod 92g against the action of the spring 92h when the discharge pressure from the supercharger exceeds Ht.sub.1. As a result, the pin 92l slides in the elongated, hole 92j formed in the link 92k so as to rotate the link 92k about the shaft 92c. Thus, the opening/closing valve 92b integrally formed with the shaft 92c is completely opened. Cooling sea water introduced from the outlet conduit 7a passes through the second bypass conduit 10 before it is discharged to the sea level 11 through the outlet conduit 7b.

FIG. 7 is an enlarged view which illustrates an opening/closing valve device 93 which is operated in accordance with the discharge pressure from the supercharger and the engine revolution speed, wherein another example of an application of the structure shown in FIG. 3 is illustrated. The cylinder 93a including a butterfly type opening/closing valve 93b is disposed in parallel to the outlet conduits 7a and 7b, the cylinder 93a being disposed in the second bypass conduit 10 which is connected to bypass the thermostat 5. A shaft 93c is an attaching shaft for attaching the opening/closing valve 93b, the shaft 93c being connected to a link 93g having an elongated hole 93f. The actuator is a solenoid 93d disposed at the end portion of a rod 93e. The operation of the solenoid 93d is controlled by a controller 93j to which a signal from a supercharger discharge pressure sensor 93k in a suction pipe 1b and a signal from an engine revolution speed sensor 93l from a flywheel 1a are supplied. The rod 93e of the solenoid 93 d is connected to the elongated hole 93f by a pin 93h. FIG. 8 is a graph which illustrates the relationship between engine revolution speed N and supercharger discharge pressure Ht. The solenoid 93d is arranged to be operated when the above-described two sensors meet conditions that the engine revolution speed is Ni and the discharge pressure from the supercharger is Hti. Any combination may, of course, be employed such that i=1, . . . , n.

As a result of the above-described setting, the solenoid 93d is operated by the controller 93j when the engine revolution speed is Ni and the discharge pressure from the supercharge is Hti. As a result, the pin 93f is rotated to completely open the opening/closing valve 93b which is integrally formed with the shaft 93c. Therefore, cooling sea water introduced from the outlet conduit 7a passes through the second bypass conduit 10 before it is discharged to the sea level 11 via the outlet conduit 7b. Although the link device shown in FIG. 7 is arranged in such a manner that the elongated hole 93f is formed in the link 93g, another structure may be employed in which the above-described elongated hole 93f is omitted, the solenoid 93d and the rod 93e are separated from each other and the end portions of the link 93g and the rod 93e and the end portions of the rod 93e and the solenoid 93d are respectively connected to each other by the pins 93h. As described above, a variety of design modifications may be performed within the scope of the present invention.

According to the present invention, there is provided an advantageous sea water cooling apparatus for a marine diesel engine which is arranged in such a manner that an opening/closing valve device is disposed in the bypass conduit, with which a satisfactory large output can be obtained even if a rapid accelerating operation is performed after the warming up operation has been performed or in a case of an operation under a large load and in which fuel can be effectively cooled by the fuel cooler.