Internal combustion engine with apparatus responsive to shortage of coolant
FIELD AND BACKGROUND OF THE INVENTION 
     The present invention relates to a water-cooled internal combustion engine, and more particularly to such an engine of the type used in a boat or other water craft. 
     A conventional water craft has a water jet type propulsion system with a water-cooled engine. The engine cooling water is sucked into the engine room from the outside of the craft through a coolant pipe, and the coolant pipe often sucks in floating debris such as pieces of nylon or vinyl sheets which block the pipe. The operator may continue operating the craft without knowing of the stoppage of coolant flow, with the result that the engine may overheat and be damaged. 
     It is a general object of this invention to provide an apparatus which responds to a shortage of coolant flow to an engine of this type, and protects the engine from damage. 
     SUMMARY OF THE INVENTION 
     Apparatus according to this invention includes air intake means connected to supply fresh air to the engine, and an exhaust system connected to discharge exhaust gas from the engine. Duct means is connected between the air intake means and the exhaust system, and a normally closed valve is provided in the duct means. Heat responsive means is provided on the engine to open the valve in response to a predetermined high temperature of the engine, whereby at least a portion of the exhaust gas is fed back through the duct means to the intake means. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other objects and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side view partially in cross section of a water jet propulsion type boat according to a first embodiment of the invention; 
     FIG. 2 is an enlarged fragmentary view in cross section of part of the boat shown in FIG. 1; and 
     FIG. 3 is a view similar to FIG. 2, but showing a second embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In FIG. 1, the boat according to the first embodiment includes a hull 1 and a cover 1a which form an enclosed engine compartment. A water-cooled engine 2 is mounted within the compartment. The engine 2 includes a conventional cylinder exhaust port (not shown) connected to a conventional exhaust manifold (not shown) and to a muffler 4, which is connected in turn to an upstream exhaust duct 6. The duct 6 is connected in turn to a water box 5 which retains the water content in the exhaust gas from the engine as will be explained. 
     A downstream exhaust duct 7 has one end 7a which opens in the water box 5 adjacent the bottom of the box, or below the end of the upstream duct 6 which is connected to the box 5. The downstream duct 7 extends upwardly from the end 7a, through the upper wall of the box 5, rearwardly of the boat, and opens at its outer end in the discharge port 19 formed through the hull 1 at the stern. 
     A branch exhaust duct 8 has one end 8a which opens into the water box 5 above the inner end 7a of the downstream duct 7. The branch duct 8 is connected through a connecting pipe 9 (FIGS. 1 and 2) to an air intake duct 10, which extends from the vicinity of the engine 2 to the outside of the hull 1 through an opening in the cover 1a. The air intake duct 10 extends through a hole in the cover and normally conveys fresh air into the engine compartment to a location adjacent the air intake of the engine. 
     As shown in FIG. 2, the cylinder 2a of the engine 2 is surrounded by a water jacket 3 which is connected to a coolant water intake tube 22 (FIG. 1) extending through a hole in the bottom of the hull 1. Water is sucked in through the tube 22, circulated through the jacket 3, and discharged through a tube 22a (FIG. 1) into the exhaust duct 6. The water mixes with the exhaust and flows to the water box 5 where it is temporarily retained. 
     The water jacket 3 has a bar-like heat sensitive member 12 extending through the wall thereof, a portion of the member 12 projecting out from the jacket 3. A rod 16 is pivotally supported at approximately its intermediate point by a pin 15 on a bracket 14 which is fixed to the pipe 9 and is therefore stationary relative to the hull 1. The lower end of the rod 16 is pivotally connected by a pin 17 to a rod 11b of a valve 11 (FIG. 2), and the valve rod 11b of the valve 11 slidably extends through a side wall of the connecting pipe 9. The body 11a of the valve 11 is urged by a spring 23 to nornmally engage a valve seat 18, which is formed in the outlet end of the branch exhaust duct 8. The upper end of the rod 16 has a block 16a fixed thereto, the block 16a being in line with the heat sensitive member 12. A predetermined gap 20 exists between the block 16a and the member 12 during the normal operation of the engine. 
     The heat sensitive member 12 may be made of aluminum or some other material which has a high heat conductivity, a high coefficient of linear expansion and a high fusion temperature. 
     In normal engine operation the valve 11 is closed and blocks any flow through the ducts 8 and 9. Normally with the valve 11 closed, the water in the water box 5 has its surface at the level of the inner end 7a of the downstream exhaust duct 7. Water normally circulates through the tubes 22 and 22a, the water jacket 3, and the duct 6 to the box 5. When the water level rises above the end 7a of the duct 7, the exhaust gas pressure in the box 5 causes any excessive amount of the water to be discharged through the duct 7 along with the exhaust gas from the upstream duct 6. 
     If the water intake tube 22 becomes blocked by a foreign body, the coolant flow stops with the result that the temperature within the engine water jacket 3 quickly rises to the order of 300° C. This excessive temperature causes the heat sensitive member 12 to expand lengthwise. The interior end 12a of the member 12 abuts a wall of the engine and therefore the member 12 cannot expand inwardly. The outer end of the member 12 therefore expands toward the right and pushes the block 20. The rod 16 pivots clockwise and opens the valve body 11a away from the seat 18. 
     Because of the resistance to the exhaust gas flow through the duct 7 caused by the water in the box 5 around the end 7a, the gas then flows through the branch duct 8, the now open valve 11, the connecting pipe 9 and into the air intake duct 10. As a result, the exhaust gas enters the engine compartment and the engine air intake, and the engine operation becomes very poor due to the shortage of oxygen. This can be noticed by the operator who should then stop and clear the water intake, or the engine will automatically stop. 
     In the embodiment shown in FIG. 3, corresponding parts are given the same reference numerals as in FIG. 2. 
     A heat sensitive unit 25 includes a cylinder 25a having an outer threaded part 25h, which engages a threaded hole in the outer wall of the engine 2. The cylinder 25a extends into the water jacket 3. The cylinder 25a has an inner end 25g of a reduced diameter which is in engagement with a recess 3a in the inner wall of the jacket 3. 
     A piston 25b is slidable within the cylinder 25a, and has an O-ring seal 25f. The piston has a piston rod 25c with a block 25d fixed to its outer end. The block 25d is aligned with the block 16a of the rod 16, and the blocks are normally spaced apart by a distance 20. 
     The cylinder 25a contains a heat sensitive fluid 25e adjacent the inner end 25g. This fluid is liquid at a normal temperature of 70°-80° C. during the normal engine operation, and vaporous at a higher or excessive engine temperature. The fluid may be water (boiling point: 100° C.) or turpentine oil (boiling point: 160° C.). Instead, the fluid may be a liquid having a high coefficient of cubical expansion, such as glycerol and paraffin oil. 
     The heat sensitive unit 25 operates by the expansion of the fluid 25e similarly to the sensor 12 in FIG. 2. The expanded fluid pushes the piston 25b outwardly and opens the valve 11, thereby causing the engine to falter or stop as previously described.