1.  Field of the Invention
The present invention relates to a waste heat recovery system for a horizontal liquid-cooled internal combustion engine, in which the engine heat absorbed by engine cooling liquid in a water jacket and the exhaust gas heat absorbed thereby in a heat exchanger for heat absorption from the exhaust gas are adapted to be recovered from the engine cooling liquid by the radiation performed in a heat exchanger for waste heat recovery. 
As for such a conventional waste heat recovery system for a liquid-cooled internal combustion engine, so far has been known the one disclosed in U.S. Pat.  No.  4,226,214. 
The conventional system is provided with a heat exchanger for heat absorption from the exhaust gas (a first heat exchanger) and a heat exchanger for waste heat recovery (a second heat exchanger) both of which are connected in series to a water jacket within an engine body so that the engine cooling liquid can circulate in order through the water jacket, the first heat exchanger and then the second heat exchanger.  Therefore,the engine cooling liquid which absorbs the heat in the water jacket also is adapted to absorb the exhaust gas heat during flowing through the first heat exchanger to reach a high temperature and then to radiate the heat retained therein to an external thermal load such a hot-water reservoir and the like through the second heat exchanger. 
In this prior art, for accomplishing a concrete waste heat recovery system, the internal combustion engine is of a vertical type, and the first heat exchanger for heat absorption from the exhaust gas and the second heat exchanger for waste heat recovery are disposed separately each other a a predetermined distance in a lateral space beside the engine body thereof.  And the cooling liquid outlet of the water jacket and the engine cooling liquid inlet of the first heat exchanger, the engine cooling liquid outlet of the first heat exchanger and the engine cooling liquid inlet of the second heat exchanger, and the engine cooling liquid outlet of the second heat exchanger and the engine cooling liquid inlet of the water jacket are connected respectively by pipes for the conduction of the engine cooling liquid. 
There are following problems associated with the above-mentioned prior art. 
(A) A large area is required for providing the waste heat recovery system because the first heat exchanger and the second heat exchanger are arranged in the lateral space beside the engine. 
(B) Since it is necessary to provide the pipes for the conduction of the engine cooling liquid at three locations, further there are following problems. 
(1) The arrangement of piping is complicated and requires much labor for assembly of the pipes.  PA1 (2) The space required for the piping gets larger, and accordingly the whole of the waste heat recovery system becomes larger.  PA1 (3) Large heat radiation losses are caused by the pipes, and the efficiency of the waste heat recovery gets worse correspondingly.  PA1 (1) Since the piping for the conduction of the engine cooling liquid is required only between the first heat exchanger and the water jacket, the arrangement of piping can be simplified remarkably.  Therefore, the assembly work of the pipes can be carried out readily, and the manufacturing cost of the waste heat recovery system can be reduced.  PA1 (2) Since the locations of providing the pipes for the conduction of the engine cooling liquid are decreased in number remarkably, the piping space can be made smaller so that the whole of the waste heat recovery system can be constructed in a smaller size.  PA1 (3) Since the heat radiation loss caused by the pipes becomes less due to the decrease of the piping locations for the conduction of the engine cooling liquid, the efficiency of the waste heat recovery in the waste heat recovery system can be improved.