Abstract:
To avoid engine idling to support cabin heating, an auxiliary coolant heater can heat engine coolant and pump it through compartment heaters or the engine cooling system. The coolant flow control system provides great flexibility in selectively distributing heated coolant for heating and engine preheating.

Description:
FIELD OF THE INVENTION  
       [0001]    This invention relates to motor vehicles, such as highway trucks, that are powered by liquid-cooled combustion engines, and that have auxiliary coolant heaters for heating engine coolant when the primary engine is off and which provide for circulating the heated coolant from the auxiliary coolant heaters to the engines for engine pre-heating and to occupant compartment heat exchangers for occupant compartment heating. 
       BACKGROUND OF THE INVENTION  
       [0002]    Cooling systems for liquid-cooled internal combustion engines conventionally comprise an engine driven pump for circulating the coolant through the cooling system and a radiator which serves to sink heat from the system to the environment. For engines and engine cooling systems used on a motor vehicle some of this heat may be diverted to the motor vehicle&#39;s passenger compartment during cool weather to heat the compartment for the comfort of the occupants. A heat exchanger or “core” through which coolant may be selectively circulated from the engine cooling system provides a way to divert engine heat to the cab for the comfort of the occupants. 
         [0003]    Certain motor vehicles, such as large trucks, have occupant compartments (cabs) that include a driver&#39;s compartment and a sleeper compartment behind the driver&#39;s compartment for use by the driver when not on duty or by a relief driver. It has been expedient in some applications to provide a second core or heat exchanger in the sleeper compartment to better distribute heat through the cab. In the past truck drivers often left the vehicle&#39;s main engine running at idle to provide heated coolant for circulation to the passenger and sleeper compartment cores to provide cold weather heating while the vehicle was parked. This had the secondary benefit of keeping the engine warm and avoiding the need for cold restarts, which are notoriously difficult on compression ignition engines. It was also widely recognized that this practice wasted fuel and contributed unnecessarily to air pollution because internal combustion engines running at idle expend too much energy overcoming the engine&#39;s parasitic losses for the amount of useful heat produced. As a result the practice of idling a vehicle&#39;s primary engine for extended periods to provide heating (or energy for cooling) has been prohibited in many areas. 
         [0004]    However, providing climate control on board parked vehicles and pre-heating engines for easier cold weather starts remain valid concerns. Accordingly the art teaches the use of on-board auxiliary coolant heaters which can provide ample heat for these functions without running the engine and incurring the engine&#39;s parasitic losses. This is sometimes referred to as “no-idle” heating. One brand of commercially available heaters offers sizes whose heat output range from 5,500 BTU to 120,000 BTU and can run on the gasoline or diesel fuel that is carried by the vehicle. Examples of patents describing similar systems, or related approaches, include U.S. Pat. No. 5,333,678 (describing an auxiliary engine which has sufficient capacity to efficiently run an air conditioner compressor or an electric generator) and U.S. Pat. No. 5,901,780 (a no-idle system). Also of interest is U.S. Patent Application Publication 2007/0063062 for a no-idle system, which is assigned to the assignee of the present application and incorporated herein by reference. 
         [0005]    A typical auxiliary coolant heater is reasonably compact and contains components necessary to heat (a burner) and circulate (a pump) engine coolant while the engine is off. The heater may provide heat at different selectable levels, and may be under the control of an associated control unit to maintain a set temperature. When occupant compartment heating is called for, a coolant pump starts circulating coolant through a heat exchanger. A heating device heats the coolant as it circulates so that heated coolant flows out of the heater. 
       SUMMARY OF THE INVENTION  
       [0006]    The present invention relates to a coolant circuit for a motor vehicle which provides for selective circulation of coolant through an on-board auxiliary coolant heater, a primary (main cabin) heater core, at least a first secondary or auxiliary (sleeper compartment) heater core, an engine cooling system, or to selected combinations of these elements. Valves are distributed through the coolant circuit allowing the selective isolation from the circuit of selected sections of the coolant circuit. A coolant flow controller, which is preferably integrated with a controller programmed for handling cabin environmental control, has control over the auxiliary coolant heater (and its attendant auxiliary pump) and the positions of the various valves. For environmental controller the flow controller may be connected to sensors providing temperature indications for the various sections of the cabin as well as coolant temperature. The coolant flow controller is coupled to receive indication of main engine operation, which will determine whether an engine coolant pump is operating. 
         [0007]    The possible combinations of circulation flow routes are determined to some extent on the operating state of the heat sources. Four states are contemplated: (1) auxiliary heater running and providing heat to pre-heat main engine which is off; (2) main engine off with auxiliary heater running to provide cabin heat; (3) main engine and auxiliary heater running; and (4) main engine on and auxiliary heater off. In state (1) the various valves are set to cut off flow to the main and auxiliary cabin heating cores but to allow circulation through the engine cooling system. In state (2) the valves controlling flow to the cabin heater cores are “modulated”, that is opened and closed in alternating fashion, to provide flow through the auxiliary and main heater cores to maintain the desired temperature in the passenger cabin. In some embodiments the valve for the main heater core may simply be closed and temperature control implemented through the auxiliary core. The valve controlling flow through the engine cooling path is also modulated to maintain engine temperature at a minimum threshold. Coolant is reverse circulated through the cores. In state (3) the engine is on but coolant temperature is measured to be below a desired minimum threshold, and as a consequence the auxiliary heater remains on. Here valves are set to isolate the engine cooling circuit from the cabin heating circuit and the auxiliary heater provides all the heat available for the front and rear auxiliary cores. Isolation of the two sub-circuits from one another prevents the engine coolant pump from damaging the auxiliary pump, both of which will be running. Coolant is reverse circulated through the cores. In state (4) the engine is on and coolant temperature in the engine coolant system sub-circuit is sufficiently high to support heating of the cabin. The valve to the auxiliary heater will be closed and the valves to the front and auxiliary cores modulated as required by temperature settings. A default state (5) may be inferred in which the engine is off and the auxiliary heater is off. It is conceivable here that the auxiliary pump may be operated and the valves set to promote flushing or cleaning of the circulation system without operation of the engine. 
         [0008]    The foregoing, along with further features and advantages of the invention, will be seen in the following disclosure of a presently preferred embodiment of the invention depicting the best mode contemplated at this time for carrying out the invention. This specification includes a drawing, now briefly described as follows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]      FIG. 1  is a side view of a truck with a sleeper cab and an auxiliary heating unit. 
           [0010]      FIG. 2  is a schematic diagram showing the coolant circuit of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0011]      FIG. 1  shows a truck  10  equipped with an auxiliary heating unit  20  for supplying heated coolant to heat exchangers installed in a driver&#39;s cab  12  and a sleep compartment  14 . Auxiliary heating unit  20  uses fuel from a vehicle fuel tank  16  and is mounted with the fuel tank on the truck chassis  18 . 
         [0012]      FIG. 2  schematically illustrates a coolant flow circuit  30  having two major sub-parts, an engine coolant circulation subsystem  31  and a cabin heating subsystem  33 . The engine coolant circulation subsystem  31  has as its primary function the extraction of heat from an internal combustion engine  32 . In normal operation, excess engine heat is typically sunk to the environment through a radiator (part of cooling system  36 ), but some of the heat may be diverted to provide heat to cab  12  and sleep compartment  14 . The engine coolant circulation subsystem  31  includes an engine driven pump  42  which forces coolant to circulate through the engine and cooling system elements  36 . A valve  52  is connected to an outlet to a port from the engine or cooling system elements  36  allowing a portion of the coolant flow to be diverted by pipes to heat exchangers in the vehicle&#39;s cabin. Valve  52  is under the control of a climate controller  62 . 
         [0013]    The auxiliary heat source  20  includes a fuel fired heater  34  and an auxiliary pump  44 . Heater  34  provides a burner and a heat exchanger through which engine coolant can be drawn (or forced) for heating. Auxiliary pump  44  delivers coolant under pressure to circulation lines of the coolant flow circuit  30  where it may be selectively routed depending upon current demands for heating, which may include preheat of engine  32  for starting, defrosting demands prior to a cold start, or maintaining cabin heat during an extended period during which engine  32  is not run. A valve  54  is provided at an outlet from the fuel fired heater  34  and pump  44  to prevent the circulation of coolant through the heater and pump under certain circumstances. An electrical motor  46  is provided as the prime mover of auxiliary pump  44 . Actuation of the valve  54  (or more properly a solenoid controlling the opening and closing of the valve) and the motor  46  are under the control of climate controller  62 . 
         [0014]    Located within a passenger cabin are a front main heater  38  and a rear main heater  40 . Heater  38  may also be referred to the primary heater or core and the rear main heater  40  may be referred to as a sleeper compartment or auxiliary heater core. The flow of coolant through heater cores  38  and  40  is controlled by the opening and closing of valves  56  and  58 , respectively, under the control of climate controller  62 . It may be observed here that the primary and auxiliary heaters  38 ,  40 , are supplied with coolant from either the engine cooling subsystem  31  or by the fuel fired heater  34 . While to be supplied with coolant from either source requires opening of implicated valve  56  or  58 , the cores  38 ,  40  are never supplied concurrently from both sources of heated coolant. When supplied with coolant from the engine cooling subsystem  31  the flow of coolant is from the IN ports to the OUT ports of cores  38 ,  40 . When supplied with coolant from the fuel fired heater  34  the flow of coolant passes into the heaters  38 ,  40  from the outlet ports to the inlet ports (reverse flow). 
         [0015]    A climate controller  62 , illustrated here as connected to the various valves and to auxiliary motor  46  for the control thereof, controls the operation of pump  44  (by control of motor  46 ), the supply of fuel to fuel fired heater  34  (which may implicate more general vehicle control functions  60  if operation of a fuel pump is required), and the opening or closing of valves  52 ,  54 ,  56  and  58 . Climate controller  62  operates in response to user requests for heat for any purpose, such as windshield defrosting or sleep compartment heating and potentially the temperature selected for such heating. Climate controller  62  also operates responsively to sensor inputs, such as a passenger compartment temperature sensor (included in package  64 ). Additionally the climate controller operates responsively to data received from a vehicle control system  60 , which includes engine  32  operating status (the climate controller needs to know if pump  42  is running) and coolant temperature. While the connections from the climate controller  62  to the various controlled elements is shown as being direct, it may occur through other control system agencies. In other words, the control functions depicted are functional rather than directly reflective of the precise control architecture. For example, climate controller  62  may be a program running on a general purpose vehicle body computer. 
         [0016]    The possible configurations of the coolant flow circuit  30  are set by which of valves  52 ,  54 ,  56  and  58  are open or closed. The selection of which valves are open or closed (or modulated between the two states or set in a partially open state) is determined to some extent on the operating state of the heat sources  32 ,  34 . Four states are contemplated: (1) auxiliary heater  34  running and providing heat to pre-heat the main engine  32  which is off; (2) main engine  32  off with auxiliary heater  34  running to provide cabin heat; (3) main engine  32  and auxiliary heater  34  both running; and (4) main engine  32  on and auxiliary heater  34  off. 
         [0017]    In state (1) the various valves are set to cut off flow to the main and auxiliary cabin heating cores  38 ,  40  but to allow circulation through the engine cooling sub-system  31 . In state (2) the valves  56 ,  58  controlling flow to the cabin heater cores  38 ,  40  are “modulated”, that is cycled between opened and closed position, potentially in an alternating manner, to provide flow through the auxiliary and main heater cores to maintain the desired temperature in the passenger cabin. In some embodiments the valve  56  for the main heater core  38  may simply be closed and temperature control implemented through the auxiliary core. The valve  52  controlling flow through the engine cooling path is also modulated to maintain engine temperature at a minimum threshold. Coolant is reverse circulated through the cores  38 ,  40 . In state (3) the engine  32  is on but coolant temperature is measured to be below a desired minimum threshold, and as a consequence the auxiliary heater  34  remains on. Here valve  52  is closed to isolate the engine cooling circuit  31  from the cabin heating circuit  33  and the auxiliary heater  34  provides all the heat available for the front and rear auxiliary cores  38 ,  40 . Isolation of the two sub-circuits from one another prevents the engine coolant pump  42  from damaging the auxiliary pump  44 , both of which will be running. Coolant is reverse circulated through the cores. In state (4) the engine  32  is on and coolant temperature in the engine coolant system sub-circuit  31  is sufficiently high to support heating of the cabin. The valve  54  at the outlet from the fuel fired auxiliary heater  34  is closed and the valves  56 ,  58  to the front and auxiliary cores  38 ,  40  modulated as required by temperature settings. A default state (5) may be inferred in which the engine  32  is off and the auxiliary heater  34  is off. It is conceivable here that the auxiliary pump  44  may be operated and the valves set to promote flushing or cleaning of the circulation system without operation of the engine  32 . 
         [0018]    The present invention is by no means limited to the five states described, and in concept is extendable to an extended cab which provides zone heating (that is to say, has a plurality of auxiliary cores). The owner of vehicles can, within limits of conflicting pump operation, determine the flow of coolant. Defrosting operations can be completed before starting a vehicle, saving idle time. 
         [0019]    While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention apply to all embodiments falling within the scope of the following claims.