Communications: electrical – Condition responsive indicating system – Specific condition
Reexamination Certificate
2002-02-21
2004-07-27
Lieu, Julie (Department: 2632)
Communications: electrical
Condition responsive indicating system
Specific condition
C340S425500, C340S573100, C454S069000, C454S070000, C454S075000
Reexamination Certificate
active
06768423
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not applicable.
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
BACKGROUND OF THE INVENTION
While the present invention may be employed in several different off-highway applications, in order to simplify this explanation, the present invention will be described in the context of an exemplary agricultural tractor and associated cab.
Today, in farming, as in other industries, competitive pressures have forced farmers to search for ways in which to increase efficiency and productivity. One obvious way to increase efficiency and productivity is to use better and more efficient equipment such as state of the art agricultural tractors or combines. A properly configured tractor appreciably increases the speed with which farmers can plant, till, fertilize and harvest.
One other way in which to increase efficiency and productivity is to employ highly specialized equipment to perform certain farming tasks. For instance, some specialized tractors are equipped with sprayers or other chemical spreading implements that apply pesticides and other noxious products within fields extremely efficiently.
Unfortunately, state of the art tractors are relatively expensive and therefore, in order to justify the costs associated with such tractors, even though the tractors reduce the time required to perform various tasks, farmers must spread the costs of such equipment over increasingly larger enterprises. In farming, a larger enterprise typically translates, at least in part, into farming more acreage and, not surprisingly, farming more acreage typically requires a greater time commitment on the part of the farmer.
In the case of specialized equipment such as sprayer equipped tractors and the like, high costs associated with that equipment and limited uses for the equipment renders it difficult for some farmers to purchase their own such equipment. Instead, a segment of the service industry has evolved around specialized types of equipment where a single owner purchases such equipment and provides services to many farmers within an area so that, again, the cost of the equipment is spread out among many farmers and their acreage.
Because farmers and special service providers are spending greater amounts of time in their tractor cabs, cab comfort has become a relatively important feature in new tractor configuration. Thus, new tractors are typically fitted with state of the art cabs including ergonomically designed seating and controls, better lines of sight and cab space conditioning systems that control temperature, air circulation and humidity.
In addition to the features described above, the industry has also recognized that air quality within the cab space is important to operator comfort and health and also to overall system efficiency. To this end, in many applications, agricultural tractors operate in environments that include high concentrations of airborne dirt and dust. Moreover, where a tractor implement is used to spray or apply a noxious chemical, portions (e.g., droplets or particles) of the noxious chemicals often become airborne and can be inhaled by a tractor operator. Hereinafter airborne particles within an environment will collectively be referred to as “contaminants”.
Inhaling contaminants can cause discomfort over short periods of time and, over long periods of time, can lead to other medical symptoms. Moreover, contaminants have been known to accumulate on heating and cooling system components and reduce both efficiency and effectiveness, thereby further reducing operator comfort.
To minimize contaminants (e.g., dirt, dust, etc.) within the cab space, it is well known to provide a completely enclosed cab and an air circulation system that takes in and filters “fresh” outside air from the ambient, heats or cools the air via an atmosphere control system and circulates the conditioned air within the cab via one or more pressurization blowers/fans. Preferably, cab air pressure is maintained above a threshold pressure that is slightly higher than atmospheric pressure (i.e., at least a few millimeters of head of water). The pressure differential between the ambient and threshold pressure inhibits entry of contaminants into the cab through, for example, imperfectly sealed doors or windows.
To increase cooling and heating efficiency, many tractor air conditioning systems will include two separate fans. In two fan systems, a first fan is typically positioned downstream of the air inlet and filter for drawing fresh air into the conditioning system from the outside ambient while a second recirculating fan is positioned downstream of a system inlet located within the cab for drawing air into the conditioning system from within the cab. The recirculating fan, as the name implies, recirculates air from within the cab through the conditioning unit. In two fan systems, the recirculated and fresh air are combined within the conditioning unit prior to being directed into the cab space. Because the recirculated air is already generally at the temperature and humidity level required inside the cab space, the system capacity required to condition the recirculated air is relatively less than the system capacity required to condition fresh air and therefore overall conditioning efficiency is increased.
Unfortunately, under certain circumstances, a cab conditioning system is rendered incapable of maintaining a cab pressure that is greater than the ambient pressure. For instance, over time, cab door and window seals deteriorate and air escapes there through at an unexpectedly high rate thereby reducing cab pressure appreciably. As another instance, “fresh” air filters (i.e., filters that clean air drawn in from the outside ambient) often become clogged thereby starving the fans of inlet air and reducing cab space air pressure. As yet another example, inadvertent placement of any item in front of a blower outlet port can cause a reduction in cab pressure. Other potential causes of cab pressure drop include malfunctioning fans, improperly positioned air louvers, slightly open doors or windows, an item (e.g., a seat belt) stuck within a closed door, etc.
One solution for maintaining a desired cab pressure in spite of some of the causes of pressure drop described above has been to facilitate either manual or automatic fan speed adjustment. To this end, pressure sensors have been developed that compare ambient and cab pressures and generate alarm signals indicating when the cab pressure dips below a threshold pressure that is slightly above the ambient pressure. In the case of manually adjustable systems, the alarm signals are fed to indicators (i.e., a small light) within the cab and, when an indicator is activated, the operator is warned of the pressure problem. An operator's manual may advise to adjust the fan speed or to modify the positions of louvers within the system plenum and duct sub-system to increase air flow.
In the case of automatically adjustable systems, the alarm signals are fed to a controller that adjusts fan speed either up or down or louver positions to maintain the cab pressure above the threshold pressure thereby maintaining cab space-ambient pressure differential yet minimizing required fresh air filtering. One exemplary automatic fan speed adjustment system is described in U.S. Pat. No. 4,581,988 (hereinafter “the '988 patent”) which issued on Apr. 15, 1986 and which is entitled “Protective Device for Work in Polluted Environment”. The '988 patent also teaches that, after increasing fan speed, if cab pressure remains below the threshold pressure, the controller activates an indicator (e.g., a small light) to warn the operator that the automatic corrective action has failed to maintain the cab space-ambient pressure differential.
In either of the manual or automatic blower speed adjustment cases, if an alarm condition occurs despite maximum fan speed, the tractor operator is supposed to recognize that the intake filter is clogged and take steps to unclog th
Doescher Robert D.
Kennedy Peter H.
Leupold Alan G.
Case Corporation
Lieu Julie
Stader John William
Webb Collin A.
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