Abstract:
An auxiliary power unit for providing power and HVAC to a vehicle. The auxiliary power unit is mounted to the vehicle in a variety of ways, but such that it can be readily moved away from the vehicle for service and maintenance. The power unit has a removable condenser and fan assembly that can be mounted to the power unit or remote from the human occupied portion of the vehicle. The power unit also including a programmable engine control unit for controlling and monitoring various aspects of the operation of the power unit and the vehicle. The power unit having a user interface that enables in-vehicle control of the engine control unit and remote control the engine control unit. The engine control unit monitoring when excessive power requirements of the power unit exists and limiting the air conditioning services of the power unit until the excessive power requirements no longer exists.

Description:
BRIEF DESCRIPTION OF THE INVENTION 
       [0001]    The present invention is related to systems for providing auxiliary power to long-haul trucks and similar types of transportation vehicles, and more particularly to a novel power unit that provides enough energy to supply concurrent loads, that does not need to actively interface with the main vehicle engine, that can be easily installed and maintained, that requires a minimal amount of space, that adds a minimum amount of weight to the vehicle, and that enables intelligent management of the power unit. 
       BACKGROUND OF THE INVENTION 
       [0002]    Transport trucks that haul goods over great distances in Europe, the Americas and other parts of the world are often referred to as long-haul trucks. In addition to a bed, the cabins of long-haul trucks are often configured to include microwaves, air conditioners, heaters, refrigerators, televisions, stereos and other electric appliances that require significant amounts of power. Long-haul trucks or big rigs will travel hundreds of miles in a day, over many days, often stopping only long enough to allow the driver to eat and take care of personal necessities and to rest and sleep, but when they do, many drivers want to use two or more of these appliances at the same time, such as an air conditioner, microwave, and television. Such conveniences are very important to many drivers, and given the increasing shortage of long-haul truck drivers, truck fleet owners are seeking new ways to attract drivers by providing a more luxurious cabin environment. Some trucking fleets have up to 100% turnover from year to year because the drivers are not satisfied with the life style provided by the fleet company. Yet, it costs a trucking company at least three thousand dollars to train new drivers, even if they have prior experience, so obviously, the quality of life of the driver is a key to success in the industry. 
         [0003]    When a long-haul truck does need to stop, the driver might be able to do so at a truck stop, which is a specialized facility for providing fuel, maintenance, parking and convenience services. At other times, the trucks will stop wherever they can safely do so, such as at roadsides, rest stops and fueling stations. Although some truck stops provide auxiliary power tethers to the trucks, most drivers prefer to stop when and where it proves to be most convenient and to idle their main engines while stopped to provide power to the cabin of the truck. In the United States, a typical long-haul truck idles 2,500 hours per year, with the main engine consuming as much as 1.2 gallons per hour. As fuel prices increase, however, it is getting prohibitively expensive for drivers to idle the main engines for hours at a time. At a fuel cost of $3.25 per gallon, idling the main truck engine costs as much as $9,750 per year. Furthermore, many countries are instituting laws that make it illegal to idle a truck engine for extended periods of time to cut down on air pollution. Idling the engine for hours also decreases the amount of time between engine overhauls without increasing the productivity of the vehicle. 
         [0004]    Accordingly, a number of companies have begun to supply auxiliary power units (APUs) to provide climate control and 120-volt power, to cut back on fuel consumption and air pollution, to reduce operating hours on the main vehicle engine, and to improve driver comfort and quality of life when on the road. A typical APU consumes about 0.2-0.3 gallons per hour, with significantly lower annual maintenance costs, thereby saving drivers/truck owners more than $6,900 per year in fuel costs alone. In the European Union, where long-haul trucks only idle about 1,800 hours per year, but fuel costs much more per gallon, the idle cost savings alone are over $8,500 per year. 
         [0005]    The APUs currently on the market, however, share certain features and disadvantages. For example, most APUs use small diesel engines for power, but depending on the size of those engines, they may be able to provide only a limited amount of DC power and BTUs/hour for air conditioning and heating. Likewise, many of these engines are directly connected to the main engine so as to share main engine coolant, which can void warranties and prevent maintenance services from being available until the APU is removed. Some APUs do not provide for AC power because they do not include a generator, while others are noisy, cost too much to maintain, are too large or heavy, or do not provide for easy management and monitoring of the unit by the driver or the fleet owner. One of the biggest shortcomings of existing APUs is that they lack the ability to provide for concurrent power loads, meaning that drivers often have to manually shut off one electrical appliance or cooling/heating source when they want to use something else. In very cold or hot environments, this factor significantly detracts from the quality of the driver&#39;s life and therefore the attractiveness of the APU. 
     
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0006]      FIG. 1  is a perspective view of the front and left side (when facing the APU from the side of the truck) of the APU in its service/maintenance position; 
           [0007]      FIG. 2  is a perspective view of the back and right side of the APU with an environmental cover and co-located condenser and fan; 
           [0008]      FIG. 3  is a perspective view of the back and right side of the APU with the environmental cover, but without the co-located condenser and fan; 
           [0009]      FIG. 4  is a perspective view of the front and right side of the APU with the environmental cover and the optional step assembly; 
           [0010]      FIG. 5  is a perspective view of the front and right side of the frame assembly illustrating a through-the-frame rail installation; 
           [0011]      FIG. 6  is a perspective view of the front and right side of the frame assembly illustrating a frame rail bracket installation; 
           [0012]      FIG. 7  is a perspective view of the front and right side of the frame assembly illustrating an installation for pre-drilled frame rails; 
           [0013]      FIG. 8  is a block diagram illustrating the interconnection between the ECU, the ECU user interface, the main engine battery, the APU engine, and the cabin HVAC system; 
           [0014]      FIG. 9  is a block diagram illustrating the interaction between the APU engine and the cabin HVAC system; 
           [0015]      FIG. 10  is a plan view of the ECU user interface; 
           [0016]      FIG. 11  is a flow chart illustrating the initial start-up operation of the ECU; 
           [0017]      FIG. 12  is a flow chart illustrating some basic operations of the ECU user interface of  FIG. 10 ; 
           [0018]      FIGS. 13   a ,  13   b  and  13   c  illustrate additional displays corresponding to operational conditions for the ECU user interface; 
           [0019]      FIG. 14  is a flow chart illustrating the battery monitoring operation of the ECU; 
           [0020]      FIGS. 15   a ,  15   b  and  15   c  are flow charts illustrating the sensor monitoring operation of the ECU; and 
           [0021]      FIG. 16  is a flow chart illustrating the load management operation of the ECU. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    The present invention relates to auxiliary power units, and in particular to auxiliary power units for long-haul trucks. In the preferred embodiment of the present invention, the auxiliary power unit (APU) has a lateral dimension of up to approximately 62 centimeters or 24.5 inches, which is small enough to enable it to be mounted in a variety of positions behind the cabin of the truck without interfering with or taking away space from other components of the truck, although APU&#39;s of many different sizes could also be utilized in a similar fashion. Typically, the APU would be mounted close to the truck cabin on one of the two frame rails of the truck, as illustrated in  FIGS. 5 ,  6  and  7 , but the APU could also be mounted between the frame rails or to some other part of the truck. 
         [0023]    Mounting the APU to one of the frame rails provides a very stable mounting environment for the APU due to the structural integrity of the frame rails. This mounting environment also enables easier installation and access to the APU for maintenance and service. Mounting the APU close to the cabin can reduce the cost of the installation by reducing the length of the umbilical cord (described further below) between the APU and the truck cabin where the main controller for the APU is located. In the preferred embodiment of the present invention, a frame rail mounted APU is disclosed that facilitates access for maintenance and service, as further illustrated in  FIGS. 1-7 . 
         [0024]      FIG. 1  is a perspective view of the front and left side of APU  10  when viewed facing the side of the truck to which the APU  10  is mounted. The APU  10  includes the APU engine  12 , which is a two or three cylinder diesel engine mounted to a frame assembly  14 , which includes a sliding component  16 . The frame assembly  14  is attached to the frame rail  15  of the truck, but the sliding component  16  enables the entire diesel engine  12  to be pulled away from the truck and easily accessed by anyone needing to service the engine. 
         [0025]      FIG. 1  illustrates the APU engine  12  when the sliding component  16  has been pulled away from the frame assembly  14 , such as when it is being serviced. In order for the engine  12  to be pulled away from the truck on the sliding component  16 , certain mechanical and electrical components need to be designed to facilitate this type of movement without breaking down over a number of years, such as the electrical wiring, hoses, exhaust pipes and other similar components. For example, the electrical wiring between the APU  10  and the truck cabin is provided through a spring-shaped umbilical cord consisting of power wires and communication wires. The spring shape of the cord enables it to stretch out when the APU is pulled away from the truck for service, and to shrink back into a smaller size when the APU is in its normal operating position, all without putting undue stress on the wires within the cord. Likewise, the exhaust pipe is connected with a flexible metal hose and a quick-fit connector, rather than welded in place. 
         [0026]    As noted, the APU engine  12  is typically a two or three cylinder diesel engine capable of generating approximately 10-30 horsepower at varying revolutions per minute, such as the Yanmar™ TNV Series-1 engines, although other types and sizes of engines could be utilized. A diesel engine of the indicated power is preferred due to environmental concerns (reduced emissions and noise), economics (better fuel economy while providing more than adequate power) and driver convenience (most long-haul trucks utilize diesel engines, thereby allowing the main engine and the APU to be fueled at the same time). Also, most truck owner/operators prefer to link the APU to the main gas tank(s) for the truck, rather than carry an additional tank for the APU, so using common fuel under such circumstances is essential. It would be preferable, obviously, to provide a separate storage tank for the APU, if the APU engine  12  used a fuel that could not be used by the main truck engine, although this would add significantly to the cost of installing the APU. 
         [0027]    As illustrated in  FIG. 1 , some of the major visible components of the engine  12  include a water/coolant radiator  18 , an air cleaner  20 , and fuel filters  22  on the right-hand side of the engine. At the front of the engine  12 , driven by the serpentine belt  24  are the engine flywheel  26 , the air conditioning compressor  28 , the AC power generator  30 , and the belt tensionor  31 . The DC power alternator  32  is shown on the back left-hand side of the engine  12 , as is the exhaust pipe  33 . 
         [0028]    As further illustrated in  FIG. 1 , the backside of the air conditioning condenser and fan  34  is shown. A perspective view of the front and right side of the condenser and fan  34  is illustrated in  FIG. 2 . The condenser and fan  34  need not be co-located with the engine  12 , if space in the area of the APU installation is at a premium, or if the owner/operator prefers to move the condenser and fan  34  as far away from the truck cabin as possible so as to reduce noise inside the cabin. 
         [0029]    In such cases, as illustrated in  FIG. 3 , the condenser and fan could be removed from the frame assembly  14 , with the resulting opening being covered by the plate  38 . The coolant lines from the compressor  28  would then be run to wherever the condenser and fan had been relocated in order for the air conditioning system to operate properly. The condenser and fan  34  works in conjunction with the compressor  28  to provide approximately 26,000 BTU/hr of air conditioning for the cabin of the truck when the APU  10  is being utilized in place of the truck&#39;s main engine. The generator  30  is configured to provide between 3.7 Kw to 6.0 Kw of AC power, while the alternator  32  is configure to provide approximately 55 Amp of DC power, although different levels of cooling and power could be configured. 
         [0030]    In the preferred embodiment of the invention, the cabin is also provided with approximately 26,000 BTU/hr of heat through use of heated coolant from the radiator and a heater core. Heat for the engine  12 , for starting and running in cold climates, is provided by a block heater. In  FIG. 9 , the interaction between the APU engine and the cabin HVAC system will be further described. Also, as further described below with respect to the ECU, air conditioning and heating (HVAC) can be automatically or manually controlled. 
         [0031]      FIGS. 2 and 3  also illustrate the APU  10  covered by its environmental shell  36 , which further reduces the level of noise produced by the APU engine  12 .  FIGS. 2 and 3  show the APU  10  as positioned in its normal operating position. The environmental shell  36  provides protection to the APU engine  12  when the truck is on the road, while allowing sufficient air to move through the shell, such as through screen  40 . A variety of different shells could be used depending on the owner of the truck and the location of the APU  10 . Owner operated trucks that have the APU  10  installed in a visible location may want a visually appealing cover, such as diamond plate metal or chromed metal. When the APU  10  is not visible, or the owner of the truck is less concerned with appearance, a less expensive thermoplastic (or similar type of material) could be used. 
         [0032]    As previously noted, sliding component  16  of the frame assembly  14  enables the entire APU engine  12  to slide out from its operating position on the rollers of the sliding component  16  when it is necessary to maintain and service the APU  10 . To prevent the APU engine  12  from sliding out during operation, the sliding component and engine need to be locked into position, using bolts or some similar form of fixation. The bolt heads should preferably be located at the front of the APU so they can be easily accessed and removed when maintenance or service is required. The environmental shell  36  could also be bolted down, or the tie downs  42  on either side of the shell, connecting the frame assembly  14  to the environmental shell  36 , could be utilized to provide a quick release mechanism for the shell. 
         [0033]      FIGS. 2 and 3  further illustrate a step assembly  44  that could be affixed to the APU  10 , which is better illustrated in  FIG. 4 . The step assembly is optional, but when provided, enables someone to climb the steps on the APU  10  to get on top of the APU  10  or the upper portion of the truck. 
         [0034]    As previously noted, in the preferred embodiment of the present invention, the APU  10  is mounted to the frame rail  15  of the truck.  FIGS. 5 ,  6  and  7  illustrate three ways in which such mounting is achieved. In  FIG. 5 , the frame assembly  14  is affixed to the frame rail  15  by a series of bolts  50  and nuts  52 . The bolts  50  are inserted into holes  53  that have to be drilled through the frame rail  15  for the purpose of mounting the APU  10 . In some applications, it may be desirable to distance the frame assembly  14  from the frame rail, for example to provide extra space for the condenser and fan  34  when that item is mounted to the APU  10  instead of in a remote location. In such cases, different length spacers  54  could be utilized between the bolts  50  and nuts  52 . When utilizing spacers  54  to create additional space for the APU  10 , caution must be exercised to prevent the APU  10  from extending too far away from the side of the truck, lest it collide with another object when the truck passes by that object. 
         [0035]    Some truck owners object to drilling holes in the frame rails out of concern for the structural integrity of the rails or due to a general unwillingness to make any permanent alteration to the truck&#39;s body. For fleet operators, business arrangements regarding the ownership and/or financing of the trucks can lead to long delays and special permissions being required in order to drill holes in the frame rails. In such cases, the bracket arrangement illustrated in  FIG. 6  can be utilized. As shown in  FIG. 6 , a front bracket  60  is attached to a rear bracket  61 , with the frame rail  15  situated in-between the brackets, by bolts  62  and nuts  64 . The frame assembly  14  is then affixed to the front bracket  60  by the bolts  66  and the nuts  68 . As discussed in  FIG. 5 , spacers  70  could also be utilized to provide extra space for the APU  10 . A wide variety of different means of attaching the frame assembly  14  to the frame rails  15  or the truck could also be utilized. 
         [0036]    In many European countries, the frame rail  15  of the truck is pre-drilled with holes for a number of different reasons, including mounting accessory equipment such as an APU.  FIG. 7  illustrates an example of a pre-drilled frame rail  15 , where the pre-drilled holes do not necessarily line up with the mounting components of the frame assembly  14 . In such a case, conversion brackets  72  would be utilized to form an interface between frame assembly  14  and the frame rail  15 . For example, the frame assembly  14  would be bolted to one side of bracket  72 , with holes in that one side of the bracket designed to line up with holes in the frame assembly  14 , while the other side of bracket  72  would be bolted to the frame rail  15 , with holes in that other side of the bracket designed to line up with holes in the frame rail  15 . 
         [0037]    The APU  10  and other aspects of the invention are controlled by an engine control unit (ECU) or engine management system (EMS), which is a microprocessor controlled electronic device that enables programmed or external control of the APU engine  12  and other electronically controlled components. ECU&#39;s are commonly used to control vehicle engines and are well known in the art. The ECU includes a variety of electrical components on a printed circuit board, including the aforementioned microprocessor that processes inputs from the engine sensors in real time and controls the hardware (including all of the electro-optical components of the APU, including the in-cabin HVAC system) in accordance with operator inputs and/or programmed instructions in the form of software or firmware. The typical ECU of an engine can read many different sensors associated with the engine and use that information to control various aspects of the engine&#39;s operation. This might include the ignition systems of the engine so as to improve fuel efficiency, regulate power, and lower pollution levels. The ECU can also compensate for many engine operation variables, such as ambient temperature, humidity, altitude, and fuel octane ratings. 
         [0038]    As shown in  FIG. 8 , with respect to the present invention, the ECU  80  is utilized to control various operational aspects of the APU engine  12 , as well as the main engine battery  82  of the truck, and the truck&#39;s in-cabin HVAC system  84  associated with the APU. The ECU  80  is in turn partly or fully controlled by the ECU user interface and control system  86 . Preferably, the ECU user interface and control system  86  is multifunctional, depending on who is using it and how the various interfaces to the control system  86  are provided. For example, the control system  86  can have an electro-mechanical user interface in the cabin of the truck that can be accessed by the driver of the truck. This type of user interface for the control system  86  utilizes a simple visual display or electronic touch screen and/or a series of basic tact switches that allow the truck driver to control some basic functions of the APU  10  through the ECU  80 . An example of a user interface with an alphanumeric display and tact switches is further illustrated in  FIG. 10 . Since many truck drivers are older and less comfortable with electronic interfaces than many younger drivers, they may prefer toggle switches, rotary switches and encoders, which are the switches typically utilized in modern automobiles and trucks used to control radios and heating/cooling systems. 
         [0039]    In addition to the electro-mechanical user interface, one or more additional types of interfaces, such as a USB interface, are preferably provided, with any and all types of user interfaces being referred to herein as a user interface unless otherwise stated. The advantage of the USB interface is that it will enable direct and remote connection of a computer to the ECU  80 . A directly connected computer could be utilized when performing maintenance and service on the truck, or when first installing or upgrading the APU  10 . Remote computer connections, for example, through a wireless Ethernet connection to the ECU  80 , would provide long-range remote diagnosis and maintenance on the APU  10 , as well as computerized setup, upgrade, testing and diagnosis of the APU  10 . Additional wireless connections could be provided through an Internet connection, a Bluetooth connection or even through a cell phone network. Drivers could even be provided with some sort of wireless remote control device, like for a television set, which would enable them to perform simple operations while sitting in a diner near their truck. 
         [0040]    While the driver&#39;s user interface might be structured to only allow the driver to control some very basic operations, such as turning the APU on and off, setting the temperature for the air conditioning or heating within the truck cabin, turning a fan on or off, and perhaps checking on certain basic maintenance items, such as whether the APU is in need of oil, computer-based user interfaces could provide a broader range of control options. Irrespectively of the control means, all such control devices would perform certain similar functions, such as setting operating times and conditions, and providing input/output data associated with usage, service and support information. 
         [0041]    The broader range of access and control provided by remote computers enables some unique features associated with the APU  10 . For example, a different level of access could be provided to a truck owner (other than the driver) or to fleet operator, thereby enabling the owner/operator to monitor the truck, the APU  10  and to control both to some degree. The owner/operator could limit the high or low temperatures that could be selected by the driver, or the amount of time the APU is allowed to run, or perform system checks to make sure the APU is not in need of service or maintenance. Likewise, the owner/operator could set certain controls that could not be overridden by the driver (or only overridden in case of emergency with the proper code), such as when the APU is turned on. For example, some drivers may not want to use the APU, preferring instead to idle the main truck engine, but the owner/operator might want the APU used instead to save money and to cut down on the operating time of the main truck engine. In some fleet trucks, the owner/operator may even prefer to prevent the driver from having any control over the APU through a user interface at all, leaving all such control for preprogrammed operation or remote control by the fleet operator. 
         [0042]    The driver/owner/operator could program the APU to turn on and off at scheduled times, such as turning the APU on for one hour every morning when the truck is not in use. In other cases, the owner/operator could use the programming of the APU to control the driver. For example, the owner/operator could set the APU user interface  86  to turn the APU  10  on after the truck has idled for more than five minutes, to see whether the main truck engine is still running, and if necessary to turn off the main truck engine. Providing a wiring connection to the ignition of the truck and the truck&#39;s main battery would readily enable this function. Monitoring the battery would tell the owner/operator whether the main truck engine was still running, thereby enabling the owner/operator to remotely kill and disable the ignition of the truck. 
         [0043]    As previously noted, remote control of the control system  86  would also enable the owner/operator to perform less nefarious activities, such as monitor oil and coolant levels, perform other diagnostics, perform remote upgrades and maintenance, etc., or to even communicate with the truck driver through the in-truck user interface. Diagnostics provided by the ECU would include various fault codes that correspond to typical engine faults that can either be stored in a log when they occur or remotely transmitted to a central control facility while the truck is on the road. Usage patterns could also be recorded or transmitted to enable fleet operators to facilitate budgeting and planning, or to prevent overuse or abuse. Any of these different levels of control would be associated with different levels of access, such as through a user name and password, such that the driver would have one level of access and control, the operator a second level of access and control, the owner a third level, and the manufacturer or service provider for the APU a fourth level. 
         [0044]    The driver and/or the owner/operator could also utilize the thermostatic temperature control features of the system so as to automate the temperature of the cabin, such as setting it at 72 degrees no matter what the external conditions might be. Likewise, thermostatic control could also allow the driver to set different temperature settings for different times of the day, such as when he/she first gets up, during normal operating times, or when the driver goes to bed. 
         [0045]    To better explain the temperature control features of the APU, reference is now made to  FIG. 9 , where the cabin HVAC system  84  is explained in detail. The cabin HVAC system  84  is part of the APU  10  and is located within or in close proximity to the cabin of the truck so that it can efficiently transfer hot and cold air into the cabin as required. It is important to note that the APU  10  of the present invention is “passive” to both the main engine of the truck and to the HVAC system associated with that main engine. In other words, the APU  10  (including the HVAC system) does not rely upon any major subsystem or component of the main truck for operation, such as the coolant, refrigerant and oil lines, the HVAC system, the electrical system, etc. The APU  10  can be configured to connect to the truck&#39;s electrical system to provide back-up power and recharge of the truck&#39;s battery or to kill the truck&#39;s engine, but the APU  10  does not rely upon any such connection for its own operation. 
         [0046]    To provide heat to the cabin of the truck, hot water is routed out of the radiator of the APU engine  12  to an electro-mechanical valve  90  within the cabin HVAC  84  and then to a heater coil  92 . A blower fan, not shown in  FIG. 9 , blows air through the heater coil and into the cabin of the truck to provide heat. Control of heat within the truck is controlled by the valve  90 , which is in turn controlled by the user interface and control system  86 . When a higher temperature is selected by the driver (or remotely) using the control system  86 , the valve  90  is opened further. Likewise, when a lower temperature is desired, the valve  90  may be further closed, or the fan speed could be lowered. 
         [0047]    In extremely cold climates, such as Alaska, parts of the United Stated, Canada and Europe, an additional heating feature might be required to warm the engine. Inserting an electric heater inside the radiator coolant hose of the APU engine  12  provides this feature. Providing power to the electric heater heats the coolant within the hose and makes it easier for the engine of the APU to start in cold weather. 
         [0048]    The cabin HVAC system  84  provides air conditioning within the cabin of the truck in a similar fashion. The APU engine  12  drives the engine flywheel  26 , which is connected to the air conditioning compressor  28  by the serpentine belt  24 . The air conditioning compressor, which is basically a pump, is responsible for compressing and transferring refrigerant gas to the condenser  34 . The intake or suction side of the compressor  28  draws refrigerant gas from the outlet of the evaporator  94 , further explained below. That refrigerant gas is then compressed and sent to the condenser  34 , where it can transfer the heat that is absorbed from the inside of the vehicle. 
         [0049]    The condenser  34  is like a radiator. It is designed to radiate heat. As previously noted, it can be located in a variety of different locations relative to the APU engine  12  so as to improve air flow through the condenser  34  and to reduce noise from the condenser fan near the cabin of the truck. As hot compressed gasses are introduced into the condenser  34 , they are cooled off. As the gas cools, it condenses and exits the condenser  34  as a high-pressure liquid. This high-pressure liquid is then routed to the receiver-drier  96 , which is designed to separate gas and liquid and to remove moisture and filter out dirt from the refrigerant. The refrigerant is routed from the receiver-drier  96  to the electro-mechanical expansion valve  98 , which can sense both temperature and pressure and can therefore be used to regulate the flow of refrigerant to the evaporator  94 . Hence, to control the air conditioning within the cabin of the truck, the ECU  80  regulates the operation of the expansion valve  98  through the controls specified by the user interface and control system  86 . 
         [0050]    The evaporator  94  serves as the heat absorption component of the cabin HVAC system  84 . Its primary duty is to remove heat from inside the cabin and to dehumidify the air inside the cabin. As warm air is sucked out of the cabin by the fan (not shown), it travels through the aluminum fins of the cooler evaporator coil, the moisture contained in the air condenses on its surface. And, as refrigerant enters the evaporator and warm air passes through the evaporator fins, the refrigerant boils, causing it to absorb large amounts of heat, which is then carried off with the refrigerant to air conditioning compressor  28 . As the heat is absorbed from the air blowing through the evaporator that air is cooled and in return blown back into the cabin of the truck. 
         [0051]    As previously noted, the ECU  80  is controlled through operation of the user interface and control system  86 .  FIG. 10  illustrates an example of an in-truck user interface  100 . So as to reduce environmental stress and in order to consolidate the location of the various aspects of the control system  86  and the ECU  80 , these two components would be preferably collocated, and referred to herein collectively as the control system  86 , within the cabin of the truck in a chassis of some type. The control system  86  would be contained within a plastic or metal box that would be mounted in a convenient location somewhere within the cabin of the truck, and connected to the APU engine  12 , the cabin HVAC  84  and the other components of the APU  10  through various wires, although wireless interconnections could also be utilized. The ECU could also be mounted within a separate box somewhere within the cabin and inaccessible to the driver. 
         [0052]    Within either the ECU box or the control system box, would be the microprocessor or controller of the ECU that would interface to the user interface  100 . This user interface would preferably be mounted to the front of one of the boxes within the cabin and be comprised of a series of buttons  102 , a speaker  104  and a display panel  106 . The buttons  102  enable the user to scroll through a series of displayed instructions or results and to make necessary selections. The buttons  102  also enable the user to start and stop the APU engine  12 , select air conditioning or heating, control a fan, turn the temperature in the cabin up or down, and access a main menu system on the display  106 . As previously noted, many different types of controls can be utilized in place of buttons, such as dials, knobs, and a wide variety of switches. As shown in  FIG. 10 , the buttons  102  are tact switches that provide a small amount of tactile feedback to the user when operated. Additional feedback could be provided in the form of some tone or audible message to the user to indicate that a button  102  has been fully depressed when making a selection. This tone would be routed through the speaker  104 . 
         [0053]    One of the buttons  102  on the user interface  100  is the start/stop button, which is used to turn the APU engine  12  on and off. When the APU is not running and the start/stop button is selected, the APU engine  12  will be started, and vice versa, when the button is selected when the APU engine  12  is running, then the APU engine will be stopped. However, before the APU engine can be started or stopped through control of the user interface  100 , the ECU needs to be running. Normally, the ECU is booted up when power is provided to the APU system, such as through a battery or through the truck&#39;s electrical system. 
         [0054]    To enhance the functionality of the APU  10  in many different markets around the world, the ECU is preferably power universal, in that it will operate with different electrical systems, such as 12 volt DC and 60 Hz and 120 volt AC systems in North America and 24 volt DC and 50 Hz and 220 volt AC systems in other parts of the world. To achieve this feature, the ECU would need to be able to sense when the input power to the ECU changes so the ECU can operate in either environment without having to have different ECUs. 
         [0055]    The control system  86  would also preferably include a real time clock that would enable timed runs of the APU, the current time to be displayed on the display  106 , the APU engine hours to be tracked for maintenance purposes, and for time-stamped logs to be created. The time-stamped logs could be used to log events such as failures, warnings, run time intervals, telemetry, etc. The control system  86  would also preferably include a means of connecting the J1939 bus that is common to most modern tractor/trailer trucks. This bus controls various sub-systems within the truck and could be used by the APU  10  to likewise interface with and control these same systems, such as the running of the main truck engine, the recharging of the battery, etc. 
         [0056]    As previously noted, the APU  10  could receive power from a battery, such as the main truck engine battery or a separate battery just for the APU  10 . Likewise, a backup battery could be provided within the control system  86  box to keep the ECU and the clock running even when power is lost from the other batteries on the truck. When power is provided to the ECU, it will perform a boot up operation  110  similar to that illustrated in  FIG. 11 . In the first step  112 , the program or programs for the ECU are loaded into its computer processor. 
         [0057]    Once these programs are loaded, the display  106  would display some type of display, step  114 , such as the one shown in  FIG. 10 , to allow an operator to know that the ECU has booted up and is operational. A bleep or similar type of tone might also be provided through the speaker  104 . A different, but similar, display and tone might be provided if a computer or other type of device was controlling the ECU remotely. The ECU would also start a number of internal monitoring subroutines or threads, such as the FET sensor monitoring thread  116  and the battery monitoring thread  118 . Once these processes have been started, the system would check to make sure the APU was running, step  119 , and exit to the main mode of operation to figure out what to do next, step  120 . 
         [0058]      FIG. 12  is a flow chart illustrating the basic operation of the user interface  100 , including typical display screens that are displayed during the ECU&#39;s operation. When the ECU is booted up and processes to step  119 , or when the ECU is activated from its sleep mode, the ECU shifts to its main mode of operation, step  120 . In the main mode, the ECU  84  first determines whether the APU  10  is running, step  119 , as previously illustrated in  FIG. 11 . If it is not running, the display  106  will indicate that the APU  10  has stopped and will indicate the total amount of time the APU  10  has run since last serviced, step  122 . Instead of indicating when the APU  10  was last serviced, other types of displayed information is also possible, such as when the APU  10  was stopped, how many total hours it has run since last overhauled, etc. 
         [0059]    If the user does not press one of the buttons  102 , as shown in  FIG. 10 , then the display will remain at step  122  until the APU  10  is started. If the user presses either the left or right arrow buttons on the display  106 , then the display will toggle through additional displays. For example, pushing the right arrow button will cause the display to show the time and date, step  124 . The time and date illustrated in  FIG. 12  is for illustration purposes only and is not intended to represent an operational date of the present invention. Pushing the right arrow button again will cause the display to show the maintenance that is currently required, if any, step  126 . Likewise, when at step  122 , pushing the left arrow button would have caused the display to toggle to step  126 , and if pushed again, then step  124 , and again, then step  122 , etc. 
         [0060]    If the APU  10  is running at step  119 , then the display will indicate the APU  10  is running, and indicate the number of hours it has run since last serviced (when reset), step  128 , or some other indication of time as indicated above. After a predetermined period of time, or when the right arrow button is pressed, the display  106  would toggle to the next display, step  130 , which shows the current coolant temperature. In time, or upon selection of the right arrow button again, the display would show the oil pressure in pounds per square inch (psi), step  132 . Subsequent displays include the generator voltage and frequency, step  134 , the time and date, step  136 , any warning signals, step  138 , and any required maintenance, step  140 . Warnings and maintenance displays could also be the default displays illustrated when any failure has occurred or any maintenance is required. For example, if the APU  10  is running, the first display could be the warning display, step  138 , so the user immediately knows that a failure has occurred, such as the alternator failing to charge. Usage of the left arrow button could likewise cause the displays to toggle between each of the displays from steps  128 - 140 . 
         [0061]      FIG. 12  is only representative of what some of the displays for the user interface  100  could be and how this user interface  100  could operate, but it need not include these exact displays or operate in just the manner illustrated above. As previously noted, if the user interface is connected to an external computer, many additional controls and therefore display options would be available. Irrespective of the user interface utilized to interact with the control system, some of the likely additional displays would include those illustrated in  FIGS. 13   a - 13   c .  FIG. 13   a  illustrates a display  142  that would be provided when the APU engine  12  is in the process of being started. Selection of the appropriate arrow button among buttons  102  would either result in this operation being canceled or the APU being started. 
         [0062]      FIG. 13   b  illustrates some of the additional displays that would be provided while operating the cabin HVAC system. For example, when the AC/Heat button among buttons  102  is pressed, the display would toggle between display  144  for air conditioning and display  146  for heat. Pushing the select button while either of these displays is on the display  106  would cause the corresponding HVAC function to be selected. Likewise, selection of the fan button would generate the fan setting display  148 , while selection of the Temp Up or Temp Down would generate the temperature setting display  150 . 
         [0063]      FIG. 13   c  illustrates additional displays associated with control of the battery charging functions of the APU  10 . Display  152  would be displayed when the user was attempting to determine or set the charge threshold for the battery. Display  154  would likewise be displayed to show the user where the voltage threshold was set. As these displays indicate, an additional function of the APU  10  is to provide back up charging support for the main battery of the truck. One of the most common assistance calls received from big rig trucks is for a dead battery. Batteries may discharge overnight when the truck is parked because a light is left on within the cabin, or for many other reasons. When the APU  10  is installed, dead batteries can be avoided through use of the battery monitoring functions of the ECU  80 . It should also be noted that the APU  10  could be utilized as a stand-alone power source for emergency use and similar types of situations. To be utilized in this manner, it would be necessary to interface the power generation functions of the APU  10  with the external device to be powered. Preferably, the APU  10  is configured to easily allow such interface. 
         [0064]    As previously noted with reference to  FIG. 11 , step  118  initiates a subroutine or thread that monitors the battery of the truck, or any other battery that might be installed on the truck, including the battery for the APU  10 . As illustrated in  FIG. 14 , initiation of this thread, step  160 , provokes the ECU  80  to determine if the battery voltage is low, step  162 . Obviously, if multiple different batteries were being monitored, this step  162  may be asked for each battery independently, or different battery monitoring threads could be run for each battery. Irrespective of the battery being checked, if the battery voltage is not low, the subroutine will move to step  164  to wait for some N period of time and then return to step  160  to start the monitoring process again, step  166 . 
         [0065]    If the battery voltage is low in step  162 , the ECU  80  will then check to see if the APU  10  is running, step  168 . If the APU  10  is already running and the battery is low anyway, there is a high probability that something else is wrong with the APU  10  or the battery, which could be handled by the ECU  80  in a number of different ways. The ECU could simply shut the APU  10  down until the problem was investigated and resolved. Alternatively, the user could select a different approach that first provides a warning to the driver before doing anything else. Hence, in step  170 , if the APU  10  is running and the user has not set a warning for when the battery voltage is low, the ECU shuts the APU  10  down, step  172 . 
         [0066]    If the warning on low battery voltage has been selected, however, the ECU will issue a warning, step  174 , that is appropriate for that condition, such as “Low Battery Voltage,” on the display  106  of the user interface, before moving on to step  164  and returning to the beginning of the thread, step  166 . If back at step  168  it was determined that the APU  10  was not running, then a different approach could be taken. In this case, if desired, the user could have selected an auto start option that would cause the APU  10  to automatically start under such conditions. If the auto start feature is enabled, step  176 , the ECU  80  would first check to make sure that the cover switch was not on, step  178 , and if it was not, then it would start the APU  10 , step  180 . The ECU checks to make sure that the cover switch is not on as a safety precaution because the cover switch is only on when the cover  36  of the APU engine  12  is open. Obviously, it would not be desirable to have the APU engine  12  automatically started while the cover is open and someone is performing maintenance on the APU engine  12  or some other component of the system, such as a fan. If the auto start feature is not enabled, the ECU  80  might just issue a warning that the battery voltage is low, step  174 , and restart the process, step  166 . 
         [0067]    In addition to monitoring the battery voltage conditions, the ECU  80  also monitors many other sensors and systems of the APU  10  during its operation. For example,  FIGS. 15   a  through  15   c  illustrate the operation of the FET sensor monitoring thread or subroutine, step  118 , referenced in  FIG. 11 . From step  118 , the ECU would initiate a number of different threads, including one thread for monitoring the AC power generator  30  and a second thread for monitoring oil pressure within the APU engine  12 . In step  190 , the ECU first seeks to determine if the frequency of power being generated by the generator  30  exceeds a predetermined maximum frequency called “overspeed Hz.” The frequency of the AC power generator is being monitored to determine if the APU engine  12  is being overtaxed or malfunctioning. If the frequency is too high, this is a sign that the generator  30  might be malfunctioning, so the ECU will shut the APU  10  down, step  192 , until the fault can be evaluated. 
         [0068]    Likewise, if the frequency is too low, below the “underspeed Hz,” step  194 , the generator  30  might be malfunctioning in a different way, so the ECU will again shut the APU  10  down, step  192 , until the fault can be evaluated. If the frequency of the generator  30  is neither too high nor too low, the ECU will nevertheless check to see if the frequency of the generator has not dropped below a nominal operating frequency, step  196 . The most likely cause of the frequency of the generator  30  dropping below the nominal frequency is too many electrical systems drawing power from the generator  30  at the same time and taxing the APU engine  12 . When this occurs, the ECU will check to see if load management is enabled, step  198 , and if so, the ECU will initiate the load management subroutine, step  200 , which is further illustrated with reference to  FIG. 16  below. If the generator  30  frequency is within the nominal range or load management is not enabled, the ECU will continue the subroutine, step  202 . 
         [0069]    The ECU initiates the process of monitoring the oil pressure of the APU engine  12  by checking to make sure the oil pressure sensor is connected or operational, step  204 , and shutting the APU  10  down if it is not, step  192 . If the oil pressure sensor is connected, then the ECU will check to see if the oil pressure is low, step  206 . If the oil pressure is low, the ECU shuts the APU  10  down, but if it is not, the subroutine continues, step  202 , to the next stages of the thread, step  208 . 
         [0070]    In this next stage of the sensor monitoring thread, illustrated in  FIG. 15   b , three different sensors are monitored. The first sensor monitored is the fire safety switch, step  210 . If the safety switch is grounded, then the ECU  80  will shut the APU  10  down, step  212 . If the safety switch is open, then the ECU moves on to the next stage of the thread, step  214 . The second sensor monitored is the coolant temperature sensor. If the coolant temperature sensor is connected, step  216 , the ECU  80  will test to see if the coolant temperature is too high, step  218 . If the coolant temperature sensor is either disconnected or inoperable or the coolant temperature is too high, the ECU  80  will shut the APU  10  down, step  212 . If the coolant temperature is acceptable, the ECU  80  moves on to the next stage of the thread, step  214 . 
         [0071]    The next sensors monitored relate to the radiator  18 . If the radiator overtemp sensor is grounded, step  220 , then the ECU will move on to the next stage of the thread, step  214 . If the radiator overtemp sensor is open, step  220 , however, the ECU  80  will check to see if the air conditioning is off, step  222 , and if it is, the ECU will turn off the radiator fan, step  224 , before continuing, step  214 , to the next stages of the thread, step  226 . 
         [0072]    In  FIG. 15   c , the thread continues, step  226 , to check additional sensors and systems. If the alternator is charging, step  228 , the thread will restart at step  118 , via step  230 . If the alternator is not charging, then the ECU will check to see if the system is set to shut down when there is no charge from the alternator, step  232 , and if so, shut the APU  10  down, step  234 . If not, then the ECU will just issue a warning that the alternator is not charging, step  236 . In addition to checking certain key sensors, the thread also checks the status of each maintenance interval, such as oil changes, step  238 , and issues a warning, step  240 , should the ECU be programmed to issue warnings for the appropriate maintenance check. It should be noted that for purposes of simplifying the drawing in  FIG. 15   c , steps  238  and  240  only represent a single maintenance check, but would in fact be repeated for each and every maintenance check that might be performed. Once all of the maintenance checks had been performed, and warnings issued as necessary, the thread would start over again at step  118 . 
         [0073]    As noted with respect to  FIG. 15   a , when the AC power generator&#39;s frequency drops below a predetermined nominal frequency, and load management is enabled, the ECU  80  will enter a load management subroutine, step  200 . As illustrated in  FIG. 16 , the ECU  80  will first retest the frequency of the generator  30  to see if the frequency is still below the nominal frequency level, step  250 . If the frequency of the AC power generator  30  has returned to at least a nominal level, then the ECU will return to the start of the sensor monitoring thread, step  252 . If the frequency of the generator  30  is still below the nominal frequency level at step  250 , then the ECU  80  will disable the air conditioning compressor  28  in step  254 . The point behind this action is that the air conditioning compressor  28  creates the single largest draw on the power of the APU engine  12  and thereby reduces the power available from the AC power generator  30  when it is enabled. 
         [0074]    Most of the time, the power drawn from the generator  30  by the air conditioning compressor is not an issue and does not cause the frequency of the generator  30  to drop below a nominal level, but if the driver attempts to run one or more electrical devices in the cabin at the same time that also draw large amounts of power, such as a microwave, it can present issues. Rather than shift the responsibility to the driver to anticipate the problem and turn off the air conditioning before using other electrical devices, the ECU  80  senses the power disruption caused by the additional electrical device and immediately disables the air conditioning compressor to free up additional power from the generator. Once the compressor has been disabled, the ECU  80  needs to figure out when to enable it again so as to not adversely affect the driver&#39;s comfort within the cabin. Hence, the ECU will wait a predetermined period of time, N seconds, step  256 , before retesting the frequency from the generator, step  258 . If the additional draw has stopped and the frequency has returned to a nominal level, the ECU  80  will enable the air conditioning compressor, step  260 . Otherwise, the subroutine will return to step  254  and continue to test the system. 
         [0075]    Additional load management features include the partial disablement of the air conditioning compressor, so as to lessen the effect of turning it off completely, and some form of electronic throttle control that would enable the engine to run at a higher speed when more power is needed. 
         [0076]    The present invention, while illustrated and described in terms of a preferred embodiment and several alternatives, is not limited to the particular description contained in this specification. Additional alternative or equivalent components and steps could be used to practice the present invention.