Thermo-electric auxiliary power unit

This disclosure relates generally to an auxiliary power unit, and more particularly to an auxiliary power unit utilizing thermo-electric devices associated with an exhaust flow.

Long distance haul machines such as on-highway trucks often power on-board electric loads associated with the comfort of an operator, as the machine parks overnight. The loads, commonly termed hotel loads, can include a television, a heater/air conditioner, a refrigerator, a DVD/VHS player, lights, etc. Traditionally, hotel loads have been powered by an auxiliary power unit and/or the primary mover when operating at low idle. If the primary mover is employed to power hotel loads, large quantities of fuel are consumed causing the generation of power to be inefficient. Idling of the primary mover also generates undesired noise. Typical auxiliary power units on the market consist of a small internal combustion engine drivingly coupled to an electric generator. These auxiliary power units, although quieter and more efficient than operating the primary mover, are still sub-optimal and expensive. An alternative type of auxiliary power unit can include a thermo-electric generator, which provides electrical power generated from the primary mover\'s waste heat, such as, for example, from the primary mover\'s exhaust.

A thermo-electric generator can be placed in or near an exhaust stream of a primary mover to convert a portion of the exhaust heat to electrical power. Specifically, the exhaust heat is applied to one side of a thermo-electric material, while an opposing side of the thermo-electric material is cooled to maintain a temperature gradient across the material. The temperature gradient is used to generate a voltage potential directed to power the hotel loads.

One example of producing electrical power utilizing a thermo-electric generator is described in U.S. Patent Publication No. 2003/0223919 (“the \'919 publication”) issued to Kwak et al. on Dec. 4, 2003. The \'919 publication discloses a supplemental energy generating system having a thermo-electric generator disposed between a coolant channel and a housing. The housing encloses a catalytic substrate and defines an exhaust passage for an engine to expel waste heat/exhaust. The thermo-electric generator is positioned to be in a heat exchange relationship with the catalytic substrate and the coolant channel, and to generate an electrical current as a function of the heat exchange. A processing system connected to the thermo-electric generator processes the electrical current and generates a power output. In this configuration, as long as the engine is running, electrical power generated from the exhaust may be used to power loads.

Although the supplemental energy system of the \'919 publication may be beneficial in generating electrical power from waste heat, it may have limited use for supplying power to hotel loads. That is, because the system of the \'919 publication relies on heat generated from the exhaust of the engine, once the engine is shut off the heat quickly dissipates and little or no power may be available. And, since hotel loads require power when the main engine is shut down (i.e., at night when the vehicle is not powered), the system of the \'919 publication may not be applicable to long distance haul machines having hotel loads. The supplemental energy system of the \'919 publication may also suffer from low efficiencies due to the use of bulk thermo-electric materials (i.e., thermo-electric materials with a figure of merit less than 1).

The disclosed auxiliary power unit is directed to overcoming one or more of the shortcomings set forth above.

One aspect of the present disclosure is directed to an auxiliary power unit. The auxiliary power unit may include an exhaust passage configured to direct a flow of exhaust from a primary mover, a catalyst substrate disposed within the exhaust passage, and a heater configured to heat the catalyst substrate. The auxiliary power unit may also include a cooling jacket associated with the exhaust passage, and a thermoelectric device disposed between the cooling jacket and the exhaust passage. The thermoelectric device may be configured to generate electrical power from a temperature gradient created by the heater and the cooling jacket when the primary mover is non-operational.

Another aspect of the present disclosure is directed to a method of generating auxiliary power. The method may include generating heat to warm an exhaust treatment device and directing the heat toward a thermo-electric material when an associated primary mover is non-operational. The method may also include cooling the thermoelectric material to produce a temperature gradient. The method may further include generating electrical power from the temperature gradient.

FIG. 1 illustrates an exemplary machine 100. The machine 100 may refer to any type of fixed or mobile machine that performs some type of operation associated with a particular industry, such as, for example, mining, construction, farming, transportation, etc. Non-limiting examples of the mobile machine 100 may include on-highway trucks, earth moving vehicles, mining vehicles, agricultural vehicles, marine vessels, and/or any other type of machine. Further, the machine 100 may be conventionally powered and/or embody a hybrid-electric powered machine. For the purposes of this disclosure, the machine 100 is depicted as a long distance haul truck. It is also contemplated that the machine 100 may embody a generator set, a pump, or another stationary operation-performing machine.