Variable cooling circuit for thermoelectric generator and engine and method of control

An apparatus is provided that includes an engine, an exhaust system, and a thermoelectric generator (TEG) operatively connected to the exhaust system and configured to allow exhaust gas flow therethrough. A first radiator is operatively connected to the engine. An openable and closable engine valve is configured to open to permit coolant to circulate through the engine and the first radiator when coolant temperature is greater than a predetermined minimum coolant temperature. A first and a second valve are controllable to route cooling fluid from the TEG to the engine through coolant passages under a first set of operating conditions to establish a first cooling circuit, and from the TEG to a second radiator through at least some other coolant passages under a second set of operating conditions to establish a second cooling circuit. A method of controlling a cooling circuit is also provided.

TECHNICAL FIELD

The invention relates to a cooling circuit for an engine and for a thermoelectric generator in an exhaust system of the engine, and to a method of control thereof.

BACKGROUND OF THE INVENTION

Recovery of vehicle exhaust heat otherwise expelled from a vehicle can improve the efficiency of various vehicle systems and improve fuel economy. For example, vehicle exhaust heat has been used to warm engine coolant, especially after a cold start of the engine. Furthermore, a thermoelectric generator (TEG) can be integrated into a vehicle exhaust system to produce electrical energy from a temperature differential created by the exhaust heat and coolant. Cooling of the TEG is sometimes accomplished by directing coolant from the TEG through the engine and engine radiator. While this minimizes the number of components required in the cooling circuit, the engine heat added to the coolant reduces the temperature differential in the TEG, thus reducing the electric output of the TEG. Other known designs utilize a separate radiator, coolant pump and coolant lines for the TEG. Besides the added cost of these additional components, the heat from the TEG added to the coolant is not utilized for improving engine warm-up in such an arrangement, and system maintenance is more complex, as each of the two separate cooling circuits must be filled with coolant separately.

SUMMARY OF THE INVENTION

An apparatus is provided that uses heat from a thermoelectric generator (TEG) to warm the engine under some operating conditions, and also utilizes a separate radiator for the TEG coolant to improve TEG efficiency under operating conditions in which the engine is already warmed and is operating under a relatively high load. The apparatus includes an engine, and an exhaust system operatively connected to the engine and configured to remove exhaust gas from the engine. A TEG is operatively connected to the exhaust system and is configured to allow exhaust gas flow therethrough. A first radiator is operatively connected to the engine. An openable and closable engine valve is configured to open to permit coolant to circulate through the engine and the first radiator when coolant temperature is greater than a predetermined minimum coolant temperature. A first and a second valve are controllable to be placed in a first position to route coolant from the TEG to the engine through coolant passages under a first set of operating conditions to thereby establish a first cooling circuit, and to be placed in a second position to route coolant from the TEG to a second radiator through other coolant passages under a second set of operating conditions to thereby establish a second cooling circuit. The first cooling circuit bypasses the second radiator to utilize available coolant heat to warm the engine while relying on the engine pump to move the coolant and thus not using electric power to run an electric pump. The second cooling circuit bypasses the engine and the first radiator, and thus uses the cooling capacity of the second radiator entirely for cooling the TEG to increase the temperature differential in the TEG and corresponding electric power output of the TEG. By controlling the valves, the first circuit can be used for engine warm-up, and the second circuit can be used to maintain a sufficient temperature differential through the TEG to ensure adequate TEG electrical output under warmed engine and high engine output conditions.

Accordingly, a method of operating a cooling circuit in a vehicle having an engine and a TEG in an exhaust system includes directing coolant from the TEG to the engine and from the engine to the TEG in a first cooling circuit when coolant temperature is below a predetermined temperature and engine load is below a predetermined engine load. An engine valve is opened to further direct some of the coolant from the engine to a first radiator and from the first radiator to the engine when coolant temperature is above the predetermined temperature. Coolant is directed from the TEG to a second radiator and from the second radiator to the TEG in a second cooling circuit when engine load is above the predetermined engine load. The first cooling circuit bypasses the second radiator. The second cooling circuit bypasses the engine and the first radiator.

DESCRIPTION OF THE INVENTION

Referring to the drawings, wherein like reference numbers refer to like components,FIG. 1shows an apparatus10for a vehicle that includes an engine12with an exhaust system14. The exhaust system14includes an exhaust manifold16from which exhaust gas flows into a catalytic converter18. The exhaust gas then flows through a thermoelectric generator (TEG)20(discussed in further detail below), as illustrated with the solid arrow A running through TEG20, before exiting the apparatus10. Alternatively, a bypass valve22may be moved by an actuator24in response to a control signal from a controller34to divert some or all of the exhaust gas away from the TEG20, as represented by the phantom arrows B running through bypass passage36. The operating conditions under which the bypass valve22will be moved are discussed further below.

The TEG20is used to produce electrical energy from exhaust heat as explained herein. The TEG20has an exhaust gas inlet38and an exhaust gas outlet40which permit exhaust gas to flow through the TEG20generally in the direction of the arrow A. As is understood by those skilled in the art, the exhaust gas flows through the TEG20to heat a hot side heat sink within the TEG20. Coolant also flows through the TEG from coolant inlet port42to coolant output port44to reduce the temperature of a cold side heat sink within the TEG20. Within the TEG20, coolant flow passages may cause coolant to flow in the same direction as the exhaust flow (i.e., in the direction of arrow A) before exiting through the outlet port44. The TEG has multiple modules that contain a plurality of solid state elements able to generate electrical energy in response to a temperature differential, as is understood by those skilled in the art. Some of the exhaust heat is absorbed by the hot side heat sink. The coolant reduces the temperature of the cold side heat sink. Thus, a temperature differential is created across the TEG modules, so that the TEG20generates electrical power that may be stored or used by various vehicle operating systems.

The TEG modules within the TEG20must not exceed a maximum recommended operating temperature for extended periods of time. The maximum recommended operating temperature is referred to herein as a critical temperature TC above which the TEG20may be damaged by extreme temperature. Thus, the controller34diverts exhaust heat by actuating the bypass valve22when vehicle operating conditions indicate temperature within the TEG20may exceed the critical temperature TC. The position of the bypass valve22is determined at least in part on the expected temperature of the TEG20, which may be measured by a metal temperature sensor within the TEG22, the temperature of the exhaust gas at the exhaust gas inlet38(or just upstream thereof) as measured by a temperature sensor, engine loading as measured by engine speed in revolutions per minute (rpm) over a given period of time, manifold air flow or manifold air pressure, or other operating conditions indicative of or that may be correlated with temperature of the hot side heat sink of the TEG20.

Cooling of the TEG20is integrated in a variable cooling circuit44that may also direct coolant through the engine12, depending on the vehicle operating conditions. Specifically, the engine12is in selective fluid communication with a first radiator46, also referred to herein as an engine radiator46, and the TEG20is in selective fluid communication with the engine12or with a second radiator47, also referred to herein as a TEG radiator.

When coolant temperature is below a predetermined coolant temperature, as indicated by a coolant temperature sensor54mounted to the engine12or otherwise in operative contact with the coolant, the engine valve48is closed.FIG. 1represents the coolant flow through a first coolant flow circuit (defined below) occurring during a first set of vehicle operating conditions, i.e., when the coolant temperature is below a predetermined temperature and engine load is below a predetermined engine load. The temperature sensor54sends a sensor signal to the controller34. The controller34opens the engine valve48via a control signal to an actuator (not shown, but as is well understood in the art), if coolant temperature is above the predetermined temperature. Other means of estimating coolant temperature or of opening the engine valve48may be used instead. For example, the engine valve48may be a type of valve that automatically opens in response to temperature instead of in response to a control signal. Engine load may be determined by the controller34based on sensors that measure engine speed in revolutions per minute, throttle position, manifold air flow, manifold air pressure, or other measurable operating characteristics that may be related to engine load by an algorithm and look-up table stored in the controller34. As used herein, “engine load” is a percentage of maximum power available at a given input speed. Intake manifold air pressure is correlated with engine load and thus may be used as an indicator of engine load. A high intake manifold air pressure is indicative of high engine load, and a low intake manifold air pressure is indicative of low engine load.

When the coolant temperature is below the predetermined temperature, the controller34places a first valve56and a second valve58in respective first positions shown inFIGS. 1 and 2. A first pump60, also referred to herein as an engine pump, is run by the engine12and acts to pump coolant through the engine12whenever the engine12is running Coolant passage62permits coolant flow from the engine12, through a first branch63of second valve58when second valve58is in the first position, to coolant passage64. Fluid flows from coolant passage64through or past an electronic pump65to coolant passage66. The electronic pump65is operatively connected to the controller34and is controlled to be on only under certain operating conditions. When the coolant temperature is below the predetermined temperature, the coolant pump65is off. Coolant passage66permits coolant flow from the pump65to the coolant inlet port42. Coolant flows through the TEG20to the coolant outlet port44. Coolant passage68permits coolant flow from the TEG20to the first valve56. Coolant flows through a first branch69of the first valve56. When the first valve56is in the first position, coolant passage70permits coolant flow from the first valve56to the engine pump60, and coolant then flows back to the engine12.

Thus, the engine12, the first and second valves56,58, engine pump60, engine valve48, electronic pump65, TEG20, and coolant passages62,64,66,68and70establish a first cooling circuit under the first set of operating conditions (i.e., coolant temperature below a predetermined temperature and engine load below a predetermined load). The first cooling circuit bypasses both the first radiator46and the second radiator47. Thus, all heat carried in the coolant from the TEG20is used to warm the engine12in order to improve engine fuel economy under the first set of operating conditions.

Referring toFIG. 2, when the coolant temperature is greater than the predetermined minimum temperature, the controller34sends a signal causing the engine thermostat48to open. This causes some of the coolant flowing through the aforementioned first cooling circuit to be diverted through coolant passage50, first radiator46, and coolant passage52back to engine12. This additional circuit through the engine12, passage50, radiator46, and passage52may be considered part of the first cooling circuit as well. If the engine load is below a predetermined engine load, the controller34will not move the valves56,58from the first positions shown inFIGS. 1 and 2. Thus, the coolant heat picked up from the TEG20and the engine12will be cooled in the first radiator46, ensuring that the coolant entering the TEG20remains at a sufficiently low temperature to maintain adequate electric power output of the TEG20. The electric pump65remains off, so electric power requirements are minimized.

Referring toFIG. 3, when the engine load reaches a predetermined minimum load, the controller34switches the valves56,58to respective second positions shown inFIG. 3. This causes fluid to flow from cooling passage68through branch74to coolant passage76. Coolant passage76permits fluid flow from the valve56to second radiator47. Coolant passage78permits coolant cooled by radiator47to flow through second branch80of second valve58to coolant passage64. In the second positions ofFIG. 3, the valves56,58cause all coolant flowing through the TEG20to be diverted from the engine12and first radiator46to the second radiator47. Thus, when the valves56,58are in the second positions, the controller34turns the electric pump65on to keep coolant moving through the second cooling circuit, which includes the TEG20, coolant passage68, first valve56, coolant passage76, second radiator47, coolant passage78, second valve58, coolant passage64, electric pump65, and coolant passage66. The engine12is cooled by the first radiator46, as the engine pump60keeps coolant moving from the engine12, through open engine valve48to coolant passage50, through first radiator46, and back through coolant passage52and engine pump60to engine12. Thus, under the second set of vehicle operating conditions, in which the engine12is warmed (i.e., coolant temperature is above a predetermined minimum temperature) and engine load is above a predetermined minimum load, both radiators46,47are used for cooling, enabling the second radiator47to sufficiently lower the temperature of coolant provided to the TEG20to thereby maintain a sufficient temperature differential through the TEG20to ensure that a sufficient amount of electric power is generated by the TEG20.

Another advantage of the apparatus10is the ability to fill both the first cooling circuit and the second cooling circuit together in a single filling. A fill port90is shown in fluid communication with the engine12. The fill port90may be a pressure bottle/reservoir external to the engine12. Alternatively, the fill port90could be located on either radiator46,47. The fill port90may be positioned relatively high so as to provide an easy drain to the engine12via a hose. There may be vent hoses (with an orifice to prevent large flow) from the high point in the water jacket of engine cylinder head(s) (not shown) that run back to the fill port90to vent the fill for service. If the valves56,58are in the first position at the start of fill, they are switched to the second positions ofFIG. 3so that the coolant flow passages76,78and second radiator47are also filled by coolant addition through the fill port90. Assuming the valves56,58are electronically actuated solenoid valves, they could be manually switched during the filling procedure by applying a voltage to them (e.g., 12 volts). Alternatively, a bypass hose and manual valve could be added to connect the first and second cooling circuits around one or more of the valves56,58specifically for use during the filling procedure.

Referring toFIG. 4, a method100of controlling a cooling circuit in a vehicle is shown as a schematic flowchart. The method100is described with respect to the apparatus10ofFIGS. 1-3, but is not limited to the embodiment of the apparatus10shown. The method100is stored as an algorithm in a processor of the controller34and is carried out by the controller34. The method100begins with block102, in which operating conditions of the apparatus10are sensed. As discussed above, this may include sensing coolant temperature using the coolant temperature sensor54, sensing engine load using an engine speed sensor, a manifold air pressure or air flow sensor, or other means, and sensing an indicator of the temperature within the TEG20, such as by a metal temperature sensor within the TEG20, temperature of the exhaust gas at the exhaust gas inlet38, or just upstream thereof, engine loading as measured by engine rpm over a given period of time, or other operating conditions indicative of temperature of a hot side heat sink of the TEG20.

Based on the sensed operating conditions of block102, the method100proceeds to block104, block105, block106, or block108. If the sensed operating conditions in block102indicate that coolant temperature is below a predetermined temperature and engine load is below a predetermined load, the method100moves to block104and directs coolant from the TEG20to the engine12and from the engine12to the TEG20in the first cooling circuit defined above by positioning the first and second valves56,58in the first position as shown inFIG. 1, bypassing both the first radiator46and the second radiator47.

If the valves56,58are already in the first position ofFIG. 1, and sensed operating conditions in block102indicate that coolant temperature is above the predetermined temperature but engine load is still below the predetermined load, then the method100moves to block105to open the engine valve48and allow coolant flow from the engine12to the first radiator46and back to the engine12, still bypassing the second radiator47. Alternatively, the engine valve48may be automatically activated by temperature, not in response to a control signal sent by the controller34.

If the sensed operating conditions in block102indicate that the coolant temperature is above the predetermined temperature and engine load is above the predetermined engine load, then the method100moves to block106to position the valves56,58in the second positions ofFIG. 3, thereby directing coolant in the second cooling circuit described above from the TEG20to the second radiator47and from the second radiator47to the TEG20, bypassing the engine12and the first radiator46. The method100must also move to block107after block106to turn on the pump65in order to cause coolant to flow through the second cooling circuit.

In addition to adjusting the flow of the coolant in blocks104,105,106and107, the method100also monitors the temperature of the TEG20in block102by sensing operating conditions such as by a metal temperature sensor within the TEG20, the temperature of the exhaust gas at the exhaust gas inlet38, or just upstream thereof, as measured by a temperature sensor, engine loading as measured by engine rpm over a given period of time, or other operating conditions indicative of temperature of the hot side heat sink of the TEG20. If the sensed conditions indicate the temperature within the TEG20is above another predetermined temperature, the method100will adjust the bypass valve22in block108to direct at least a portion of the exhaust gas flow around the TEG20.

Thus, the apparatus10and method100are designed to allow rapid warm-up of the engine12to improve engine efficiency and minimize electric power requirements by directing heated coolant exiting the TEG20to the engine12, and then directing the heated engine coolant to the second radiator47when the engine12is sufficiently warmed and engine load is high enough to merit operating the electrical pump65. Utilizing the second radiator47enables a greater reduction in coolant temperature entering the TEG20, thus optimizing electrical energy production of the TEG20.