Auxiliary power unit heating system

Abstract

An engine heating system for vehicles comprising an engine, a vehicle compartment heating system including fluid conduits extending from the engine to a heating unit and extending back to the engine, an auxiliary power unit on the vehicle including an auxiliary engine having a water pump driven by the auxiliary engine including fluid conduits extending from the auxiliary engine to a second heating unit located in a compartment of the vehicle and extending back to the auxiliary engine, fluid conduits extending from the engine to the second heating unit and extending back to the engine, a valve disposed in the fluid conduit between the second heating unit and the engine, the valve capable of receiving a signal, a temperature switch for detecting a coolant temperature, the temperature switch providing a signal to operate the valve, the valve allowing coolant circulation through the second heating unit to the main engine when the main engine is in operation or the coolant temperature is greater than a predetermined temperature, and the valve closed when the main engine is not in operation or the coolant temperature is below a predetermined temperature.

1 . An engine heating system for vehicles comprising: 
 an engine;    a vehicle compartment heating system including fluid conduits extending from the engine to a heating unit and extending back to the engine;    an auxiliary power unit on the vehicle including an auxiliary engine having a water pump driven by the auxiliary engine including fluid conduits extending from the auxiliary engine to a second heating unit located in a compartment of the vehicle and extending back to the auxiliary engine;    fluid conduits extending from the engine to the second heating unit and extending back to the engine;    a valve disposed in the fluid conduit between the second heating unit and the engine, the valve capable of receiving a signal;    a temperature switch for detecting a coolant temperature, the temperature switch in electrical communication with the valve and the temperature switch energizing the valve upon detection of a predetermined coolant temperature;    the valve allowing coolant circulation through the second heating unit to the main engine when the main engine is in operation or when the coolant temperature is greater than a predetermined temperature; and    the valve closed when the main engine is not in operation or when the coolant temperature is below a predetermined temperature.    
   
   
       2 . The engine heating system as in  claim 1 , wherein the temperature switch is inoperable when the engine is in operation and the temperature switch is operable when the engine is not in operation.  
   
   
       3 . The engine heating system as in  claim 1  further comprising: 
 a relay for energizing the temperature switch; and    the relay is open during operation of the main engine.    
   
   
       4 . The engine heating system as in  claim 1 , wherein the valve is normally open.