Engine liquid cooling system

Abstract

A method of limiting pressure in a liquid cooling system of an internal combustion engine when the engine overspeeds, such as when an engine brake is applied.

What is claimed is: 
     
         1 . An internal combustion engine which comprises:
 engine structure comprising engine cylinders within which combustion of fuel occurs to generate heat, a first portion of which operates the engine and a second portion of which heats the engine structure, and internal coolant passageways through which liquid coolant circulates to absorb heat from the engine structure;   a liquid cooling system comprising a pump driven by the engine for circulating liquid coolant through the internal coolant passageways, a radiator at which heat is rejected from liquid coolant flowing through the radiator to air flowing through the radiator, a first coolant return passage for liquid coolant flow to by-pass the radiator, and a first control valve having an inlet open to a first outlet of the internal coolant passageways for controlling coolant flow from the first outlet of the internal coolant passageways through the radiator and the first coolant return passage;   a second coolant return passage for liquid coolant flow from the internal coolant passageways to by-pass both the first control valve and the radiator, the second coolant return passage comprising a second control valve having an inlet open to a second outlet of the internal coolant passageways which is separate from the first outlet of the internal coolant passageways, the second control valve controlling flow of coolant from the second outlet of the internal coolant passageways back to the pump; and   an engine controller for controlling the second control valve to control flow of coolant through the second control valve.   
     
     
         2 . The internal combustion engine as set forth in  claim 1  in which the engine controller is effective to operate the second control valve from closed to open in response to engine speed increasing to a speed greater than maximum engine operating speed within a normal engine operating speed range and from open to closed in response to engine speed decreasing to a speed less than maximum engine operating speed within the normal engine operating speed range. 
     
     
         3 . The internal combustion engine as set forth in  claim 2  including an engine brake which when applied and when combustion of fuel in the engine cylinders is temporarily stopped, causes engine speed to increase to a speed greater than the maximum engine operating speed within the normal engine operating speed range. 
     
     
         4 . The internal combustion engine as set forth in  claim 1  in which the engine controller operates the second control valve from closed to open when pressure at a location in the liquid cooling system is indicated to have become greater than a predetermined pressure and from open to closed when pressure at the a location in the liquid cooling system is indicated to have become not greater than the predetermined pressure. 
     
     
         5 . The internal combustion engine as set forth in  claim 1  in which the engine controller comprises a software logic section and maps which provide data for processing by the software logic section to control the second control valve. 
     
     
         6 . In a liquid cooling system of an internal combustion engine having a pump which is driven by the engine to circulate liquid coolant through internal coolant passageways in engine structure to absorb heat from combustion of fuel occurring within engine cylinders within the engine structure to operate the engine over a normal operating speed range up to a maximum engine operating speed, a method of limiting pressure at a location in the liquid cooling system, the method comprising:
 using a first control valve to control coolant flow from a first outlet of the internal coolant passageways through a radiator and a first coolant return passage to the pump; and   using a second control valve to control coolant flow from a second outlet of the internal coolant passageways which is separate from the first outlet of the internal coolant passageways through a second coolant return passage which returns to the pump and by-passes both the first control valve and the radiator.   
     
     
         7 . The method as set forth in  claim 6  including operating the second control valve from closed to open in response to engine speed increasing to a speed greater than maximum engine operating speed within a normal engine operating speed range and from open to closed in response to engine speed decreasing to a speed less than maximum engine operating speed within the normal engine operating speed range. 
     
     
         8 . The method as set forth in  claim 7  including applying an engine brake to cause engine speed to increase to a speed greater than maximum engine operating speed within the normal engine operating speed range.