Locomotive Cab Heating System

The present invention relates to heating systems, and more particularly, to systems for controlling heat in a locomotive cab.

Heating systems for the cabs of locomotives typically are unsophisticated, consisting of a motor driven blower, ductwork connecting the blower to the cab, and several heating elements which can be activated to heat the air supplied by the blower. With such systems, the occupant of a locomotive cab controls the temperature in the cab by adjusting the blower setting and/or adjusting a heat setting which activates one or more heating elements, roughly providing high, medium or low heat. A disadvantage with such systems is that even a high heat/high blower setting resulted in a high volume of relatively cool, high velocity air being blown into the locomotive cab through supply ducts, which is perceived to be uncomfortable by the occupants of the cab.

Accordingly, there exists a need for a locomotive cab heating system which can be easily retrofitted to replace such prior art systems, and which has improved heating performance and control. Preferably, such a system is adjustable by the operator to maintain a comfortable temperature level without the necessity of making large adjustments to the blower speed, and therefore the volume flow rate of air supplied to the cab.

The present invention is a heating system for a locomotive cab which is designed to be retrofitted onto a preexisting heating system of a type having a motor driven blower that delivers air through ducts into the cab, and which includes a plurality of individual heating units in the cab supply ductwork to heat the air delivered to the cab. Such preexisting heating systems typically include a blower having a motor that can be set by a user to a desired one of several blower speeds to vary the rate of air flow into the cab.

The present invention is a system for activating the individual heating units and monitoring the duct air temperature such that the air delivered to the cab is maintained within predetermined limits regardless of the rate of air flow (i.e., fan blower speed setting), the limits being below the preset automatic shutdown air temperature. As a result, the temperature of the air emitted from the heating ducts in the locomotive cab is maintained automatically within a comfortable range for the cab occupants, regardless of the fan blower setting.

The heating system of the present invention includes a thermistor in the supply air ductwork to the locomotive cab downstream of the heating units. The thermistor produces an analog signal which is converted to a digital signal that is read by an onboard microcontroller which controls the actuation of the heating units. The microcontroller is equipped with EEPROM memory which stores a software program that actuates groups of heating units (i.e., two, four or all six heating units in a standard six-unit system) depending upon the temperature of the air flowing through the ductwork.

Accordingly, it is an object of the present invention to provide a locomotive cab heating system in which the supply air temperature is maintained within a predetermined range; a heating system which provides automatic delivery of maximum heat to the locomotive cab for a given motor for a given air flow; a heating system which delivers air at a desired flow rate and temperature without a risk of the system shutting down as a result of overheating; a heating system in which the temperature of the air supplied to the locomotive cab is controlled without the necessity of a thermostat within the cab itself and without requiring extensive redesign and refitting of preexisting systems; and a heating system which is relatively inexpensive and can be retrofitted to existing, conventional locomotive cab heating systems.

Other objects and advantages will be apparent from the following description, the accompanying drawings and the appended claims.

FIG. 1 is a schematic diagram of the preferred embodiment of the present invention;

FIG. 2 is a schematic diagram of the interconnection of the microcontroller with the components of the invention shown in FIG. 1; and

FIG. 3 is a graphical depiction of the algorithm of the microcontroller, showing the temperature ranges and activation of the heating units of the system of FIG. 1.

As shown in FIG. 1, the locomotive cab heating system of the present invention, generally designated 10, includes a fan motor 12 which powers a fan blower 14 that discharges into a supply duct, generally designated 16, that directs air through a vent 18 into a cab 20 of a locomotive. Mounted within a straight run 22 of ductwork 16 are six heating units 24, 26, 28, 30, 32, 34 which are separately actuated. A high level shutdown thermostat 36 is also mounted in the ductwork 22 downsteam of the heating units 24-34. In addition, a thermistor 38 is also mounted adjacent to the thermostat 36. A return air duct 40 leads from the cab 20 into the intake of the fan blower 14.

As shown in FIG. 2, a micrococontroller 42 is connected to an electronics package 44 that actuates the motor 12 of the fan blower 14 (FIG. 1). The microcontroller also receives discrete switch input from a fan blower control 46, typically mounted within the cab 20 (FIG. 1). Microcontroller 42 is programmed to activate a different maximum number of heating elements 24-34 for each discrete blower speed setting. For example, for a low fan setting, the maximum number of heating elements activated may be four, or alternately six units. Microcontroller 42 also receives an analog input from the thermistor 38 (FIG. 1). Analog input from thermistor 38 is converted to a digital signal by the microcontroller 42. The microcontroller 42 also actuates heating units 24-34. Thermostat 36, which is a high level shutdown thermostat, is not connected to the microcontroller 42, but rather is connected to shut off a circuit breaker which shuts off power to the heating units 24-34 by a separate system (not shown).

The microcontroller 42 is programmed with an algorithm stored in EEPROM 48, which is part of the microcontroller 42. The algorithm is shown graphically in FIG. 3. Line A in FIG. 3 represents the temperature sensed by thermistor 38 and communicated to microcontroller 42. Line B represents the number of heating units 24-34 that are actuated by microcontroller 42 at a given time. In a preferred embodiment, groups of heating units are actuated, preferably groups of two, such as units 24, 26; 28, 30; and 32, 34 (see FIG. 1). The pairs of heating units that are actuated by microcontroller 42 are represented by the numbers along the vertical axis of the graph of FIG. 3. The horizontal ("X") axis represents an arbitrary time period of operation of the system 10.

The operation of the locomotive cab heating system 10 of the present invention is as follows. The heating system 10 is actuated by an occupant in the cab 20 and the thermistor 38 measures the ambient air temperature within the duct 16. This temperature is represented by line A and, for this example, begins at 65.degree. F. (18.degree. C.) (FIG. 3). The thermistor 38 signals the microcontroller 42 that the temperature is below a value, stored in EEPROM 48, which is the upper limit of the desired temperature range, represented by dashed line C, and accordingly, the microcontroller 42 actuates substantially all, or in this particular embodiment, all six heating units 24-34, as represented by line segment D. As the temperature rises in response to the heat input by heating units 24-34, it reaches the upper limit at 50 which intersects line C. In a preferred embodiment, this temperature is 145.degree. F. (63.degree. C.). At that time, the microcontroller shuts off one pair of heating units, such as units 32, 34, so that two pairs of heating units (or four heating units 24-30) are activated, which is represented by line segment E. A wait or monitoring period .DELTA.t transpires, typically on the order of 20-30 seconds, represented by interval F. This wait period F is a part of the algorithm and is triggered when the temperature signal by thermistor 38 reaches line C on the rise. At this time, the temperature at thermistor 38 may begin to drop, but so long as the temperature is below the line C, and above the lower temperature limit represented by broken line G (preferably 135.degree. F. (57.degree. C.)), the system maintains its current mode of operation, that is, with four heating units 24-30 activated.

When the temperature sensed by thermistor 38 drops below line G, such as at point 52, the microcontroller 42 will actuate the then unused third pair of heating units 32, 34 represented by line segment H, which results in an increase in the temperature of the air within the duct 16. Should the temperature rise above the upper limit represented by line C, such as at point 54, the system 10 again shuts down heating units 32, 34 represented by line segment 1, for another monitoring period .DELTA.t at J. After time interval J, if the temperature remains above the upper limit, represented by line C substantially all, or in this particular embodiment, all units 24-34 are shut off by microcontroller 42, a condition represented by line segment K.

When the temperature in the duct 16 drops below the temperature represented by line C, indicating a duct air temperature within the desired range, four heating units 24-30 are then actuated, represented by line segment L. Should the temperature continue to drop below the lower limit at point 56, the microcontroller 42 will then actuate the remaining two unused units 32, 34, represented by line segment M. Thereafter, if the temperature rises for any reason above the shutdown limit, represented by point 58, the shunt trip connection of thermostat 36 will shut the entire system 10 down. Such a temperature rise may be caused by a major air restriction, such as the blockage of supply air ducts to the cab 20 of the locomotive, or a failure of fan blower 14.

As shown in FIG. 3, the operation of the heating system 10 limits the supply air temperature of the heating system substantially within a predetermined temperature range, such as between 135.degree. F. and 145.degree. F. (57.degree. C. and 63.degree. C.) as shown in the figure. In the preferred embodiment, the temperature sampling occurs at periodic time intervals, on the order of 5 milliseconds, although different time intervals can be employed without departing from the scope of the invention.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise form of apparatus, and that changes may be made therein without departing from the scope of the invention.