This invention relates to pressure, temperature, and oxygen measurements and more particularly to systems for measuring truck and mining tire inflation gas oxygen concentrations, temperatures, and pressures and for predicting inflation pressure changes required to achieve targeted operating pressures.
Giant off-the-road tires, particularly those employed by earth moving and mining ore vehicles, are subjected to very heavy loads that make them susceptible to premature failure unless proper inflation gas pressures are maintained. Such tires are even subject to dangerous explosive failure if the inflation gas includes an oxygen concentration exceeding certain limits. For this reason, many mine truck operators are now using dry nitrogen as an inflation gas. Even so, trapped gases, air leaks, hydrocarbon out-gassing, and osmosis can cause a dangerous oxygen buildup inside the tires.
FIG. 1 represents a mining ore truck 10, which can weigh up to 550 tons when loaded and carries its heavy loads on only two axles. A front axle 12 has two single tires 14 mounted thereon and a rear axle 16 has two dual tires 18 (only one xe2x80x9cdualxe2x80x9d shown) mounted thereon, resulting in loads of about 50 tons per tire. A typical tire is inflated through a conventional valve stem 20 (only two shown) to an operating pressure ranging from about 85 to 185 pounds per square inch of gauge pressure (xe2x80x9cpsigxe2x80x9d) and, when operating, may have an operating temperature ranging from about 100 to 255 degrees Fahrenheit (xe2x80x9cxc2x0 F.xe2x80x9d). If the tire pressure is too high, a failure mode (explosion) may occur. However, if the tire pressure is too low, the excess heat generated may cause separation of some of the 18 to 22 tire layers after as few as 300 hours of operation, whereas such tires normally have at least a 1,000 hour operating life. Giant off-the-road tires cost about $25,000 to $30,000 each, and vehicle downtime costs at least about $500 per hour. Clearly, maintaining proper tire operating pressure is an economic and safety imperative.
Unfortunately, conventional tire pressure measurement methods require allowing the tires to cool for about eight hours before an accurate tire pressure measurement and inflation pressure adjustment can be made. The resulting costly downtime often leads to infrequent tire pressure measurements. To make matters worse, tires inflated by conventional air compressors often add water vapor and compression heating of the inflation air, causing errors between the measured and operating air pressures in the tires. Of course, conventional compressed air also includes oxygen. Moreover, off-the-road vehicle operators often add fluids to tires to inhibit rim rust and scale that otherwise makes tire removal difficult. Also, new tires are stored outdoors where they can collect rainwater, some of which inevitably remains in the tire when it is installed on a vehicle. Unfortunately, such fluids have vapor pressures that contribute to pressure measurement errors. Tires operating under these conditions are referred to as xe2x80x9cwetxe2x80x9d tires. Finally, many off-the-road vehicles operate in cold climates but are maintained in heated facilities, further complicating the tire inflation pressure problem. Unfortunately, conventional gas law equations do not provide solutions to these problems.
There are previously known apparatus and methods for solving some of the above-described problems. In particular, U.S. Pat. No. 5,452,608 for PRESSURE AND TEMPERATURE MONITORING VEHICLE TIRE PROBE WITH RIM ANCHOR MOUNTING describes a tire rim mounted sensor probe and conductor terminal apparatus for sensing the air pressure and temperature inside a tire. When the vehicle stops, a conventional electronic measuring device is electrically connected to the conductor terminal to convert the sensor probe data into pressure and temperature measurements. Unfortunately, the sensor probe is separately mounted through a hole in the rim, a disadvantage that weakens the rim and requires a relatively expensive field retrofit to every rim. If a new rim is required, it similarly has to be retrofitted, adding to the downtime of vehicle. Of course, a tire cool down period may be required to obtain usable readings.
U.S. Pat. No. 5,335,540 for TIRE MONITORING APPARATUS AND METHOD describes a tire pressure and temperature sensing apparatus that employs radio telemetry to continuously monitor tire pressure and temperature while the vehicle is a operating. However, as in the above-described patent, the pressure and temperature sensing probe is separately mounted to the rim, which has many of the above-described disadvantages. Moreover, every vehicle must carry a telemeter receiver by which the vehicle driver monitors the tire operating pressures and temperatures.
There are many other patents describing tire pressure and temperature monitoring apparatuses and methods. Some describe sensors embedded in the tires, others describe wheel hub mounted slip rings for conducting sensor data to a vehicle data processor, and still others describe complex systems for inflating and deflating tires while the vehicle is operating. However, there is no known prior method or apparatus that measures oxygen concentration or accounts for pressure measurement errors caused by air compressors, water vapor pressure, and temperature changes.
What is needed, therefore, is an accurate tire pressure, temperature, and oxygen concentration measuring system that does not require a cool down time, does not require expensive retrofitting or weakening of tire rims, accounts for sources of measurement errors, is readily transferred among tires and vehicles, and is usable on a wide variety of tire and wheel combinations.
An object of this invention is, therefore, to provide an apparatus and a method for measuring tire pressure and predicting inflation pressure changes that account for many sources of measurement errors without requiring a tire cool down period.
Another object of this invention is to provide an apparatus and a method for measuring tire pressure and temperature without resorting to expensive retrofitting or weakening of tire rims.
A further object of this invention is to provide a tire pressure and temperature measuring apparatus and a method that is readily transferable among tires and vehicles and is usable with a wide variety of tire and rim combinations.
Yet another object of this invention is to provide an apparatus and a method for measuring oxygen concentration in the inflation gas of a tire.
A first embodiment of a tire pressure and temperature measurement system of this invention adapts a Y-block to an existing valve stem. One branch of the Y-block accepts a conventional valve core and the other branch of the Y-block accepts a flexible tubular temperature sensor that leads xe2x80x9cdown the throatxe2x80x9d of the existing valve stem and into the interior of the tire. Making a measurement entails stopping the vehicle and, without a cool down period, attaching a pressure sensor to the conventional valve stem and attaching a hand-held processor to the pressure and temperature sensors. The hand-held processor reads the current tire pressure and temperature and executes a program that accounts for measured and target temperatures, vapor pressures, and gas compressibility and indicates how much pressure to add or subtract to the tire to achieve an accurate final tire operating pressure.
A second embodiment of the tire pressure and temperature measurement system employs a modified Y-block that adapts to an existing rim, angle adaptor, and extension hose of an inside dual tire. The modified Y-block receives an elongated temperature sensor with sufficient flexibility for feeding down the throat of the extension hose, bending around the corner of the angle adaptor, and protruding into the interior of the tire. Making a measurement is carried out as in the first embodiment.
A third embodiment of the tire pressure and temperature measurement system encloses pressure and temperature sensors and a battery powered telemetry transmitter inside a generally oblate protective housing, all of which is simply placed loosely within the interior of a tire when it is mounted to a rim. The telemetry transmitter battery capacity is sufficient for one year of continuous operation, which exceeds the expected tire life. In this embodiment, a telemetry receiver receives pressure and temperature data transmitted from inside the tire and conveys the data to a processor that executes the program described in the first embodiment. The telemetry receiver can be tuned to receive data from multiple tires while the vehicle is moving. Alternatively, the telemetry receiver can be adapted to receive data only from a closely adjacent tire.
A fourth embodiment of the tire pressure and temperature measurement system encloses the pressure and temperature sensors and the battery powered telemetry transmitter inside a protective U-shaped channel housing that is magnetically attached to the rim inside the tire. As in the third embodiment, the telemetry receiver receives pressure and temperature data transmitted from inside the tire and conveys the data to a processor that executes the program described in the first embodiment. The telemetry receiver can be tuned to receive data from multiple tires while the vehicle is moving. Alternatively, the telemetry receiver can be adapted to receive data only from a closely adjacent tire.
A fifth embodiment of this invention includes an oxygen sensing subsystem that detects the presence of oxygen in the tire interior and presents an alarm condition indicative of a potentially hazardous oxygen concentration. The oxygen sensing subsystem is mounted on or within the tire is preferably implemented as a part of the above described temperature and pressure monitoring embodiments. The oxygen sensing subsystem includes an oxygen sensor that generates an analog voltage corresponding to an oxygen concentration in the tire. A sensor amplifier conditions the oxygen sensor signal for presentation to a comparator that is coupled to a controller in the tire pressure and temperature measuring system. To conserve battery power, oxygen measurements are sampled on demand and/or pulsed on, sampled, and then turned off for a predetermined time period.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof that proceed with reference to the accompanying drawings.
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