Abstract:
A cooling system for a vehicle having an internal combustion engine permits rapid warm-up of the engine by the use of two electrically-operated valves in addition to a conventional thermostat. A bypass valve and a heater valve both remain closed at low coolant temperatures and engine speeds, thereby inhibiting coolant flow through the engine. A control unit opens the bypass valve to prevent cavitation in the water pump if engine speed and/or load exceeds a certain value. The heater valve is opened when a threshold engine coolant temperature is reached permitting warming of the heater matrix.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims foreign priority benefits under 35 U.S.C. §119(a)-(d) to GB 0919393.9 filed Nov. 5, 2009, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates to cooling systems for a motor vehicle having an internal combustion engine. 
     2. Background Art 
     As internal combustion engines become more fuel efficient, less waste heat is produced and consequently, the time taken to reach an optimum running temperature increases. This protracted time has a deleterious effect on fuel economy and engine wear. 
     Hence, a cooling system which reduces the time taken for a cold engine to reach its optimum running temperature would be desirable. 
     SUMMARY 
     Accordingly, in a first embodiment, the present disclosure comprises a cooling system for a motor vehicle having an internal combustion engine, said cooling system including a pump for supplying coolant to the engine, an outflow conduit for connecting the pump outlet to the engine, and a return circuit for connecting the engine to the pump inlet, wherein the return circuit comprises three branches, a first branch including a first valve, a second branch including a radiator and thermostat, and a third branch including a heater matrix, a degas tank and a second valve. 
     The second branch of the return circuit may further include an engine oil cooler. 
     The first and second valves may be controlled electronically and the cooling system includes a control unit for controlling the valves in response to an input from at least one of the following onboard vehicle devices; an engine coolant temperature sensor, an ambient air temperature sensor, a timer, a cabin heating demand sensor, an engine operating condition sensor. 
     The engine operating condition sensor may be, for example, a sensor which detects engine speed, engine load, throttle position or mass air flow into the engine. 
     To prevent damage to the pump if malfunction of the control unit were to occur, the first valve has its default position set to the closed position and the second valve to has its default position set to the open position. 
     In accordance with a second embodiment, the present disclosure includes a method of operating a cooling system for a motor vehicle having an internal combustion engine, wherein the cooling system includes a pump for supplying coolant to the engine, an outflow conduit for connecting the pump outlet to the engine, and a return circuit for connecting the engine to the pump inlet, the return circuit comprising three branches, a first branch including a first valve, a second branch including a radiator and thermostat, and a third branch including a heater matrix, a degas tank and a second valve. The method includes: opening both first and second valves for a period long enough to flush air from the system when the engine is started cold. Then, both valves are closed. At least one engine operating condition and engine coolant temperature are monitored. The first valve is closed if one engine operating condition exceeds a pre-set level; and the second valve is opened if engine coolant temperature exceeds a threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic block diagram of a cooling system in accordance with a preferred embodiment of the disclosure, 
         FIG. 2  is a chart illustrating an operating regime of a first valve which is included in the system of  FIG. 1 , and 
         FIG. 3  is a chart illustrating an operating regime of a second value which is included in the system of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     As those of ordinary skill in the art will understand, various features of the embodiments illustrated and described with reference to any one of the Figures may be combined with features illustrated in one or more other Figures to produce alternative embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of the present disclosure may be desired for particular applications or implementations. Those of ordinary skill in the art may recognize similar applications or implementations consistent with the present disclosure, e.g., ones in which components are arranged in a slightly different order than shown in the embodiments in the Figures. Those of ordinary skill in the art will recognize that the teachings of the present disclosure may be applied to other applications or implementations. 
     With reference to  FIG. 1 , a water pump  1  supplies coolant to an internal combustion engine  2  via a conduit  3  which connects the pump outlet to the engine  2 . 
     Coolant returns to the inlet side of the pump  2  via a return circuit which comprises three branches. A first branch  4  includes an electronically controllable bypass valve  5 . A second branch  6  includes a radiator  7  and thermostat  8 . A third branch  9  includes a heater matrix  10 , an engine oil cooler  11  and electronically-controllable heater/degas valve  12  and a degas tank  13  connected via a side branch  14  upstream of the heater/degas valve  12  and downstream of the oil cooler  11  and heater matrix  10 . 
     A temperature sensor  15  is provided on the engine  2  for monitoring the temperature of the coolant at the point at which it leaves the engine  2 . 
     An electronic control unit (ECU)  16  is electrically connected with the bypass valve  5  and the heater/degas valve  12  and controls opening and closing of each valve  5 ,  12 . The ECU  16  receives inputs from a timer  17 , an ambient air temperature sensor  18 , an engine speed sensor  19  and a cabin heater demand sensor  20 . A conduit  21  links the engine  2  directly with the degas tank  13 . Alternatively engine speed sensor  19  may be an engine load sensor, a throttle position sensor, or a mass airflow sensor. 
     Operation of the system of  FIG. 1  is described with particular reference to  FIGS. 2 and 3  in which  FIG. 2  shows operation of valve  5 , a first valve, and  FIG. 3  shows operation of valve  12 , a second valve, according to one example embodiment. The specific ranges in speed and temperature shown in the table and the numbers provided herein are non-limiting and merely serve to provide one example. 
     During operation, the ECU  16  constantly monitors engine coolant temperature, engine speed, ambient air temperature and cabin heat demand (as requested by the occupants of the vehicle) and is also responsive to a signal from the timer  17 . In response to these various inputs, the ECU  16  opens or closes each of the valves  5 ,  12  in accordance with a pre-set operating regime. 
     For a few seconds immediately following a cold start of the engine  2 , both valves  5 ,  12  are opened. This measure serves to flush out air that might be in the system. After ten seconds (in this example) have elapsed, as measured by the timer  17 , both valves are closed. Provided that engine speed remains relatively low, both valves  5 ,  12  remain closed. With both valves  5 ,  12  closed and the thermostat  8  also closed, there is virtually no circulation of coolant through the engine  2  and so the engine warms up quickly. However, if engine speed reaches a threshold value, say 2300 rpm in this example, then the bypass valve  5  is opened to prevent cavitation occurring in the pump  1 . If the engine speed continues to increase, say beyond 3000 rpm them the heater/degas valve  12  is also opened to ensure that no pump damage can occur. 
     If engine rpm remains within the lower limit, then both valves  5 ,  12  remain closed until the engine coolant temperature reaches an intermediate (medium) value, say 60 degrees Celsius, whereupon the bypass valve  5  is opened. This allows some coolant flow through the engine while the thermostat  8  remains shut. 
     The heater/degas valve remains closed until engine coolant temperature rises further to around 80 degrees Celsius, say, unless ambient air temperature is very low or the occupants demand some cabin heating in which case it is opened sooner. 
     Throughout the engine coolant temperature range from around 80 degrees Celsius to the point at which the thermostat opens, say 103 degrees Celsius, both valves  5 ,  12  are open, irrespective of engine speed. Hence (warm) coolant is supplied to the heater matrix and to the oil cooler for warming the cabin of the vehicle and for maintaining engine oil at an optimum temperature. 
     Once this threshold temperature of 103 degrees Celsius is exceeded and the thermostat  8  is open, the bypass valve  5  is closed allowing full flow of coolant through the radiator  7 . 
     If the engine  2  is switched off and the restarted when still hot, the bypass valve  5  is closed and the heater/degas valve is opened. 
     The default (unpowered) position of the bypass valve  5  is closed and the default (unpowered) position of the heater/degas valve  12  is open. Hence if the ECU  16  fails, the valves  5 ,  12  allow coolant to flow such that no damage to the pump  1  or a hot engine  2  can occur. 
     While the best mode has been described in detail, those familiar with the art will recognize various alternative designs and embodiments within the scope of the following claims. Where one or more embodiments have been described as providing advantages or being preferred over other embodiments and/or over prior art in regard to one or more desired characteristics, one of ordinary skill in the art will recognize that compromises may be made among various features to achieve desired system attributes, which may depend on the specific application or implementation. These attributes include, but are not limited to: cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. The embodiments described as being less desirable relative to other embodiments with respect to one or more characteristics are not outside the scope of the disclosure as claimed.