A COOLING SYSTEM OF AN INTERNAL COMBUSTION ENGINE HAVING A TURBO-CHARGER

Abstract: A water jacket in the turbo-charger is positioned at the same level or higher than a water jacket in an engine cylinder head. The turbo-charger cooling water circulation passage­ way includes a water volume or tank positioned at a level higher than the turbo-charger cooling portion, and the volume or tank is connected to a cooling water reservoir tank via a pressure relief valve which is opened when pressure in the volume or tank exceeds a predetermined value to supply cooling water to the volume or tank.

Description: The present invention relates to a cooling system of an internal combustion engine having a turbo-charger. More particularly, it relates to a system for cooling the turbo-charger by circulating a part of the engine cooling water through a cooling water circulation passageway of the turbo-charger. A turbo-charger for an internal combustion engine usually includes an exhaust turbine impeller which is exposed to and heated by the high temperature of engine exhaust gas passing through the turbo charger. Therefore, the shaft bearings of the turbo-charger are also heated because of the heat transmitted from the turbine impeller. A bearing housing of the turbo-charger is, therefore, provided with cooling water jackets in the vicinity of the turbine impeller, and when the engine is running a part of the engine cooling water is forcibly circulated therethrough to cool the bearing portions of the turbo-charger. Namely, a cooling water passage is branched from the downstream side of a water pump to introduce the cooling water into the water jackets. Therefore, when the engine is running, the cooling water is compulsorily fed into the cooling system of the turbo-charger. However, when the engine is stopped, the performance for cooling the turbo-charger depends largely on a level at which the turbo-charger is positioned, since the bearing portions thereof are then cooled by a so-called natural or gravity circulation. Consequently, if the turbo-charger is positioned lower than the cylinder head of the engine, a natural circulation is established through conventional piping for the cooling water, which cools the interior of the engine as well as the turbo-charger. However, if the turbo-charger is positioned higher than the engine cylinder, the cooling water may be boiled in the water jacket of the turbo-charger, thus filling the jackets with vapor (gas) which will prevent the circulation of the cooling water, when the engine is stopped after having been driven in a heavy load condition. Therefore, positioning the turbo-charger at a higher level than that of the engine with conventional piping for circulating cooling water causes an increase in the temperature of the bearing portions and a deterioration in the lubricant. A cooling system for the casing of a turbo-charger is described in DE―A―2 825 945. To avoid the above-mentioned problems, an electric water pump can be added exclusively for the cooling water piping of the turbo-charger, and this water pump is driven after the engine is stopped. This solution may provide effective cooling, but the electric water pump is very expensive per se, and the capacities of the alternator and battery must be increased to cope with the extra load incurred thereby. An object of the present invention is to provide a cooling system of an internal combustion engine having a turbo-charger capable of overcoming the disadvantages of the above-mentioned conventional cooling system of an engine, capable of cooling the bearing portions of the turbo-charger after the engine is stopped, capable of increasing the flexibility of the arrangement of the turbo-charger, and capable of supplying cooling water easily to the engine cooling system. According to the invention these objects are achieved by the cooling system of an internal combustion machine having a turbo-charger specified in claim 1. According to the invention, the turbo-charger cooling portion is positioned at the same level as or higher than the cylinder head cooling portion of the engine, the turbo-charger cooling water circulation passageway includes a water volume or tank positioned at a level higher than the turbo-charger cooling portion, and this volume or tank is connected to a cooling water reservoir tank via a double-function pressure relief valve, a first valve element of which is opened when the pressure in the volume or tank exceeds a predetermined value, and a second valve element of which is opened when the pressure in the volume is lower than a predetermined value, to supply cooling water to the volume. The water volume or tank is connected to the engine cooling water circulation passageway, downstream of the thermostat valve and upstream of the radiator. The outlet passage of the turbo charger cooling water circulation passageway is connected to the engine cooling water circulation passageway downstream of the radiator and upstream of the water pump. Advantageous embodiments of the invention are subject-matter of the subclaims. In the following the invention will be described in more detail with reference to the drawings. Fig. 1 is a schematic view illustrating a first embodiment of a cooling system for an internal combustion engine having a turbo-charger according to the present invention; Fig. 2 is a block diagram of the cooling system shown in Fig. 1; Fig. 3 is a cross-sectional view illustrating a portion in the vicinity of a turbine impeller in the turbo-charger; Fig. 4 is a schematic view illustrating a second embodiment of a cooling system of the present invention. In Figs. 1 and 2 illustrating a first embodiment of the present invention, there is shown a body of an internal combustion engine 1, a radiator 2, a turbo-charger 3, a thermostat valve 4, a cooling water outlet 5, a cooling water inlet 6, a water pump 30 (Fig. 2) and a bypass passage 32 (Fig. 2). An engine cooling water circulation or main passageway is filled with cooling water and comprises at least a cylinder head cooling portion 1a (Fig. 2), the thermostat valve 4 locatad at the cooling water outlet 5, the radiator 2, and the water pump 30 (Fig. 2). The engine cooling water is forcibly circulated through various portions of the engine, including the cylinder head cooling portion 1a, by the water pump 30 (Fig. 2). When the temperature of the cooling water exceeds a predetermined value, the thermostat valve 4 is opened to allow the cooling water to pass through the radiator 2 as indicated by broken line arrows in Fig. 2. When the thermostat valve 4 is closed, the cooling water flows directly through the bypass passage 32 to the water pump 30, as shown by the arrow in Fig. 2, and thus does not flow through the radiator 2. According to the present invention, the turbo-charger 3 having a cooling portion or jacket 10 (Fig. 3) is situated in such a way that the cooling portion or jacket 10 is positioned at a level higher than the cylinder head cooling portion 1a of the engine. A turbo-charger cooling water circulation passageway comprises a water hose 19 branched from the cooling water outlet 5 of the main passageway at the down stream side of the thermostat valve 4. A part of the engine cooling water passed through the interior of the engine flows from an via the water hose 19 into a water tank or volume 8 upper part 2a of the radiator 2 and then, via a water hose 9 connected to a bottom of the water tank or volume 8, into the cooling portion or jacket 10 (Fig. 3) of the turbo-charger 3, from where the cooling water flows into the cooling water inlet 6 via a hose 11. As seen from Fig. 3, the cooling portion or jacket 10 is arranged in the turbo-charger 3 in such a manner that it effectively cools a shaft bearing portion 13 adjacent to a turbine impeller 12, which is particularly subject to very high temperatures and thus tends to become very hot. The water tank or volume 8 is situated at a level higher than that of the cooling portion or jacket 10 of the turbo-charger 3. Consequently, the water hose 9 extends gradually upward from the cooling portion or jacket 10 to the bottom of the water tank or volume 8. The water tank or volume 8 is connected via a double-function pressure relief valve 14 provided at an upper wall thereof and through a hose 15 to a bottom of a cooling water reservoir tank 16 having a pressure relief port 17 at an upper portion thereof. According to the above-mentioned arrangement, when the engine is running and when the thermostat valve 4 is opened, the colling water is fed to the cooling portion or jacket 10 of the turbo-charger 3 to cool the shaft bearing portion 13 of the turbo-charger 3 by means of the water pump 30 (Fig. 2). When the engine is stopped, especially just after the engine has been driven in a heavy load condition, steam (a mixture of gas and liquid) formed from water boiled in the cooling portion or jacket 10 (Fig. 3) of the turbo-charger 3 is drawn up to the water tank or volume 8 positioned above the cooling portion or jacket 10 via the water hose 9. This sets up a syphoning action by which the cooling water in the water tank or volume 8 is fed into the cooling portion or jacket 10 of the turbo-, charger 3 also via the water hose 9, or cooling water in the cooling water inlet 5 is fed into the cooling portion or jacket 10 via the water hose 19 and the water tank or volume 8, and thus the shaft bearing portion 13 (Fig. 3) of the turbo-charger 3 is always cooled. When the pressure of the vapor or steam (gas) in the water tank or volume 8 exceeds a certain value, the pressure relief valve 14 is opened to release the gas to the cooling water reservoir tank 16. This also sets up a syphoning action whereby the water in the cooling water reservoir tank 16 is fed to the water tank or volume 8, via the hose 15, and then to the cooling portion or jacket 10 of the turbo-charger 3 via the water hose 9, and thus the cooling portion or jacket 10 is continuously filled with cooling water. Air accumulated in the upper portion 2a of the radiator 2, when the engine is stopped, can be released to the water tank or volume 8 through the hose 19. The hose 19 must extend gradually upward toward the water tank or volume 8 from the upper portion 2a of the radiator 2. When the amount of cooling water in the water tank or volume 8 is reduced, cooling water in the cooling water reservoir tank 16 is supplied to the water tank or volume 8 by a syphoning action which is effected when the double-function pressure relief valve 14 is opened in accordance with the pressure of steam (gas) in the water tank or volume 8. Thus, the cooling water is effectively supplied not only to the turbo-charger cooling water circulation passageway, but also to the engine cooling water circulation passageway. Although the size (volume) of the water tank or volume 8 depends on the size or performance of the turbo-charger 3, the size must be at least large enough to hold sufficient cooling wafer to fully cool the turbo-charger, 3 especially just after the engine is stopped, and to have a cross-sectional area at least larger than a sum of the cross-sectional areas of the water hoses 19 and 9 connected thereto. Figure 4 illustrate a second embodiment of the present invention, wherein a housing 21 of the down stream side (upper side, in Fig. 4) of the thermostat valve 4 is vertically extended in such a manner that a portion of this housing 21 serves as a water volume or tank, instead of the water tank or volume 8 which is a feature of the first embodiment (Fig. 1) of the present invention. In this embodiment, a water hose 9 extended gradually upward from the upper portion of the turbo-charger 3 and connected to a portion of the housing 21 at the down stream side (upper side, in Fig. 4) of the thermostat valve 4. The housing portion 21a above the thermostat valve 4, which is at a level higher than the upper portion 2a of the radiator 2, is connected via a double-function pressure relief valve 14 provided thereon and a hose 15 to a cooling water reservoir tank 16. In this second embodiment, a water tank or volume as shown in the first embodiment at reference numeral 8 is not necessary, but a larger space for the housing 21 is necessary, since this housing 21 must be larger than the housing for the first embodiment. In the embodiment illustrated in Fig. 4, when the engine is stopped, steam accumulated in the turbo-charger 3 is released to the housing 21. Then, when the thermostat valve 4 is open and the pressure of the steam in the housing portion 21a above the thermostat valve 4 exceeds a predetermined value, the double-function pressure relief valve 14 is opened and the steam is released to the cooling water reservoir tank 16. In the embodiments mentioned in this description, in the upper portion 2a of the radiator 2 an opening is usually provided with a cap, which is removable for filling cooling water into the radiator 2. However, this system can be a so-called sealed cooling water system, and the cap may therefore be not provided.

Claims: 1. A cooling system for an internal combustion engine having a turbo charger (3), comprising an engine cooling water circulation passageway filled with cooling water including at least a cylinder head cooling portion (1a), a water pump (30) for forcibly circulating said cooling water through said engine, and a thermostat valve (9) located at an engine cooling water outlet (5), which valve is opened to allow said cooling water to pass through a radiator (2) when the temperature of the cooling water is increased, a turbo charger cooling water circulation passageway including a turbo charger cooling portion (10) and means for supplying a part of said cooling water to said turbo charger cooling water circulation passageway and returning it from there to said engine cooling water circulation passageway, characterized in that said turbo charger cooling portion (10) is positioned at the same level or higher than said cylinder head cooling portion (1a) of the engine, that said turbo charger cooling water circulation passageway includes a water volume or tank (8; 21) positioned at a level higher than said turbo charger cooling portion (10), that said water volume or tank (8; 21) is connected to a cooling water reservoir tank (16) via a pressure relief valve (14), which is opened when the pressure in said water volume or tank (8; 21) exceeds a predetermined value and is opened to supply cooling water to said water volume or tank (8; 21), that the water volume or tank (8; 21) is connected to the engine cooling water circulation passageway, downstream of the thermostat valve (4) and upstream of the radiator (2) and that a hose (11) connects the outlet passage of the turbo charger cooling water circulation passageway to the engine cooling water circulation passageway downstream of the radiator (2) and upstream of the water pump (30). 2. A cooling system as set forth in claim 1, wherein said turbo charger cooling water circulation passageway comprises a water hose (9) extending gradually upward from said turbo charger cooling portion (10) to said water volume or tank (8; 21), so that the pressure of steam generated in said turbo charger cooling portion (10) can be relieved to said water volume or tank (8; 21). 3. A cooling system as set forth in claim 1 or 2, wherein said water volume or tank (8; 21) is connected at an upper portion thereof to said cooling water reservoir tank (16), so that air in said water volume or tank (8; 21) can be relieved to said cooling water reservoir tank (16) when the pressure in said water volume or tank (8; 21) exceeds a predetermined value. 4. A cooling system as set forth in claim 1, 2 or 3, wherein said said water volume or tank is formed in said engine cooling water outlet (5) at a position downstream of said thermostat valve (4) which position is at a level higher than said thermostat valve (4). 5. A cooling system as set forth in claim 4, wherein said said engine cooling water outlet (5) is connected to said cooling water reservoir tank (16) at a position downstream of said thermostat valve (4), which position is at a level higher than said thermostat valve (4).

Inventors: FUKUDA, TAMOTSU, HASEGAWA, MITSURU
Applicants: TOYOTA JIDOSHA KABUSHIKI KAISHA
Application year: 1985
Main classification: F01P11
IPC codes: F01P3, F02B39, F02C6, F01P11