Abstract:
A transponder-based microwave telemetry apparatus for moving machinery includes a microwave transmitter disposed outside the moving machinery to fill a chamber of the moving machinery with microwave energy. The transponder-based microwave telemetry apparatus also includes a transponder disposed inside the moving machinery for measuring a sensed condition of a part of the moving machinery and providing a modulated microwave signal that contains information on the sensed condition. The transponder-based microwave telemetry apparatus further includes a receiver disposed outside the moving machinery to separate modulated and continuous-wave signal components of the signal and extracts information from the modulated component.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to microwave telemetry and, more specifically, to a transponder-based microwave telemetry apparatus for sensing conditions in or on machinery. 
   2. Description of the Related Art 
   It is known to sense conditions in machinery such as an internal combustion engine or a torque converter for a motor vehicle. Typically, the engine includes an engine block having a plurality of cylinders and reciprocating pistons disposed in the cylinders. The pistons are reciprocated by a crankshaft via connecting rods. 
   It is desirable to monitor or sense temperature, pressure, strain, acceleration, proximity, velocity, etc. inside machinery such as the internal combustion engine. However, it becomes difficult to get the sensed conditions off of moving parts and out of enclosed areas of the engine as a reliable, usable signal and in a cost effective manner. For example, it has been proposed to bring signals out of the engine using slip rings and/or mechanical linkages. These have a number of inherent disadvantages. Slip rings are susceptible to electrical noise, which affects reliability. Mechanical linkages are difficult to install, requiring extensive modifications to the engine, and are limited as to the speeds to which they can be exposed, i.e. engine R.P.M. 
   It is also known to provide a microwave telemetry apparatus for sensing conditions. An example of such an apparatus is disclosed in U.S. Pat. No. 5,555,457 to Campbell et al., the disclosure of which is hereby incorporated by reference. In that patent, an apparatus includes a sensor to sense the interior pressure of a torque converter and generate an electrical signal representative of that pressure. The apparatus also includes a microwave transmitter located within the torque converter, which converts the electrical signal to microwave energy, which is radiated into the interior of the torque converter. The apparatus further includes a stationary receiving microwave antenna exposed to the interior of the torque converter to receive the microwaves and transmit an electrical signal corresponding the microwave energy to a remote receiving device external of the torque converter. 
   A number of techniques are currently used to measure the temperature of a piston in an internal combustion engine. For example, infrared telemetry transmits information “line-of-sight” as pulses of infrared light from the paths to a stationary photodetector disposed in the crankcase of the engine. Another example is the contact point method, which maintains continuous sliding electrical contact between the piston and the stationary contact on the engine block. Yet another example is the induction coil method that transmits information only at the top or bottom of piston travel when a moving secondary coil on the system is coupled with a stationary primary coil on the engine. Still another example is an “L-Link” or “Grasshopper” linkage, which is designed to support the information carrying wire harness from the piston to outside the engine. A further example is radio frequency telemetry, which transmits information from the piston by way of a radio transmitter mounted on the piston, which transmits waves to an antenna in the crankcase of the engine. Yet a further example is “templugs” which are small threaded plugs made of alloy steel with a special heat treatment. After exposure to elevated temperatures, the plugs will undergo an annealing process and the hardness of the plugs is measured to determine what temperature they were exposed. 
   SUMMARY OF THE INVENTION 
   It is, therefore, one object of the present invention to provide a transponder-based microwave telemetry apparatus for sensing conditions in or on moving machinery. 
   It is another object of the present invention to provide a transponder-based microwave telemetry apparatus for sensing temperature, pressure, strain, acceleration, proximity, velocity, etc., in or on moving machinery such as a piston in an internal combustion engine, or a blade element in a torque converter. 
   To achieve the foregoing objects, the present invention is a transponder-based microwave telemetry apparatus for moving machinery. The transponder-based microwave telemetry apparatus includes a microwave transmitter disposed outside the moving machinery to fill a chamber of the moving machinery with microwave energy. The transponder-based microwave telemetry apparatus also includes a transponder disposed inside the moving machinery for measuring a sensed condition of a part of the moving machinery and providing a modulated microwave signal that contains information on the sensed condition. The transponder-based microwave telemetry apparatus further includes a receiver disposed outside the moving machinery to separate modulated and continuous-wave signal components of the signal and extract information from the modulated component. 
   One advantage of the present invention is that a transponder-based microwave telemetry apparatus is provided for moving machinery such as an internal combustion engine. Another advantage of the present invention is that the transponder-based microwave telemetry apparatus has a smaller package size, no “line-of-sight” constraint, which allows more freedom in the placement of the transmitter and receiver. Yet another advantage of the present invention is that the transponder-based microwave telemetry apparatus uses an electromagnetic frequency which is relatively unaffected by any other interference in the engine and is actually enhanced by reflection within the confines of a crankcase of an internal combustion engine. Still another advantage of the present invention is that the transponder-based microwave telemetry apparatus has low power consumption, has no wires, is easy to install, supports continuous data transmissions, and experiences very little attenuation by engine oil in a crankcase of an internal combustion engine. A further advantage of the present invention is that the transponder-based microwave telemetry apparatus incorporates a transponder that shrinks the size of conventional transmitters and greatly reduces power consumption. 
   Other objects, features, and advantages of the present invention will be readily appreciated, as the same becomes better understood, after reading the subsequent description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a fragmentary elevational view of a transponder-based microwave telemetry apparatus, according to the present invention, illustrated in operational relationship with moving machinery such as an internal combustion engine. 
       FIG. 2A  is a block diagram of a transponder of the transponder-based microwave telemetry apparatus of  FIG. 1 . 
       FIG. 2B  is a circuit schematic of a transponder of the transponder-based microwave telemetry apparatus of  FIG. 1 . 
       FIG. 3  is a block diagram of the transponder-based microwave telemetry apparatus of  FIG. 1 . 
       FIG. 4  is a graph of voltage versus time for the transponder-based microwave telemetry apparatus of  FIG. 1 . 
       FIG. 5  is a block diagram of another embodiment, according to the present invention, of the transponder-based microwave telemetry apparatus of  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the drawings and in particular  FIG. 1 , one embodiment of a transponder-based microwave telemetry apparatus  10 , according to the present invention, is illustrated in operational relationship with moving machinery such as an internal combustion engine, generally indicated at  12 . The internal combustion engine  12  includes an engine block or crankcase  14  having at least one cylinder  16 . The internal combustion engine  12  also includes a piston  18  disposed and movable in the cylinder  16 . The internal combustion engine  12  includes a connecting rod  20  having one end pivotally connected to the piston  18  by suitable means such as a pin  22 . The internal combustion engine  12  also includes a rotatable crankshaft  24  connected to the end of the connecting rod  20  by suitable means such as a pin  26 . It should be appreciated that the internal combustion engine  12  is conventional and known in the art. 
   The transponder-based microwave telemetry apparatus  10  includes a transponder  28  connected to the piston  18  or connecting rod  20  by suitable means. The transponder  28  measures a sensed condition such as temperature of the piston  18  in the internal combustion engine  12  and modulates the signal received from a transceiver  32  to be described to produce a signal that contains information on the sensed condition by varying the scattering efficiency of the transponder antenna. It should be appreciated that the sensed condition may be temperature, pressure, strain, acceleration, proximity, velocity, etc. It should also be appreciated that, although an embodiment illustrating the internal combustion engine  12  is shown, the transponder-based microwave telemetry apparatus  10  may be used for sensing conditions in or on other moving machinery such as a torque converter. It should further be appreciated that the transponder  28  may be mounted anywhere that there is room on a given machine part and packaged to withstand very high g loading, shock, vibration, and temperature. 
   The transponder-based microwave telemetry apparatus  10  also includes a receiving antenna  30  having one end extending through the crankcase  14  for receiving the modulated microwave signal from the transponder  28 . The transponder-based microwave telemetry apparatus  10  includes a transceiver  32  connected to the other end of the receiving antenna  30 . The transceiver  32  is of a microwave type for receiving the modulated signal and for transmitting microwave energy. The transponder-based microwave telemetry apparatus  10  also includes a transmitting antenna  34  having one end connected to the transceiver  32  and another end extending through the crankcase  14  to fill the crankcase  14  of the internal combustion engine  12  with microwave energy from the transceiver  32 . It should be appreciated that temperature sensitive thermistors (not shown) in the piston  18  are used to sense temperature of the piston  18  and are electrically connected by suitable means such as wires (not shown) to the transponder  28 . 
   Referring to  FIG. 2A , the transponder  28  has four specific parts. The transponder  28  includes a switch  28   a , an information gathering circuit  28   b , an antenna  28   c , and a power source  28   d  such as direct or inductive current. The switch  28   a  turns the antenna  28   c  ON and OFF at a frequency determined by the information gathering circuit  28   b . It should be appreciated that the ON and OFF action of the antenna amplitude modulates the scattered component of the incoming microwave energy or carrier from the transceiver  32 . It should be appreciated that this is accomplished by switching the antenna between resonant (with high signal output) and nonresonant (with a low signal output) conditions. 
   Referring to  FIG. 2B , a circuit schematic of the transponder  28  is illustrated. The transponder  28  includes a timer chip  36 , for example a LM555CN type or AD537 Voltage-To-Frequency Converter, and a diode  38 , for example, a HP5082-2835 Schottky diode, which act as the switch  28   a . The transponder  28  also includes the power source  28   d  such as a nine-volt (9V) battery  40  and a first resistor  42  connected to one side of the diode  38 . The first resistor  42  is also connected to the timer chip  36  and has a predetermined resistance such as one kilohm. The transponder  28  includes a second resistor  44  interconnecting the other side of the diode  38  and the timer chip  36 . The second resistor  44  has a predetermined resistance such as one kilohm. The transponder  28  may include other electrical components electrically connected to the timer chip  36  such as a capacitor  46  having a predetermined capacitance of 10 nF, a third resistor  48  having a predetermined resistance such as 1 kilohm, and a fourth resistor  50  having a predetermined resistance such as 3.3 kilohm. It should be appreciated that these resistors and capacitor  46  determine the frequency at which the diode switches. It should also be appreciated that one of the resistors is a thermistor. 
   The timer chip  36  is used as the information gathering circuit  28   b  that biases the diode  38  on and off at a rate determined by the sensed signal. The diode  38  requires a predetermined voltage such as 0.5 V before it fully conducts current. The diode amplitude modulates the incoming carrier from the transmitting antenna  34  and its wire leads reradiate the AM signal to the receiving antenna  30 . The signal evolution in time and frequency domains for the transponder  28  is illustrated in  FIG. 4 . It should be appreciated that the timer chip  36  may be removed and the square wave output from the information gathering circuit connected to the diode  38 . It should also be appreciated that this alternative permits a thermistor to be removed. 
   Referring to  FIG. 3 , the transponder-based microwave telemetry apparatus  10  is diagrammatically shown. The transceiver  32  has a signal generator  32   a  to transmit a signal of 2 to 26 gigahertz (GHz), preferably 2.144199 GHZ in the embodiment illustrated, and a receiver  32   b  to receive a signal of a frequency of about 144 megahertz (MHz) and to output a signal of about 1.0 KHz. The transceiver  32  may include a first double balanced mixer  52  for a first channel of the radio frequency signal and a second double balanced mixer  54  for a second channel of the radio frequency signal. The mixers  52  and  54  can receive a radio frequency signal of about 0 to about 18 GHz. The transceiver  32  may include a frequency multiplier  56  having an output to the mixers  52  and  54  and receiving an input from the signal generator  32   a . The frequency multiplier  56  is a by twenty (20×) frequency multiplier having a FLO of 2.0 GHz. The receiver  32   b  receives the output from the mixers  52  and  54 . A spectrum analyzer  58  and an audio amplifier  60  may be connected to the output of the receiver and to each other for analyzing the microwave telemetry apparatus  10 . The spectrum analyzer  58  may be a HP3585A having a range of about 20 Hz to about 40 MHz and the audio amplifier  60  may be an electro-voice Model E-V 1282. 
   In operation, the signal generator of the transceiver  32  transmits a microwave frequency, sinusoidal carrier to the transponder  28 . The transponder  28  modulates the carrier&#39;s amplitude with the square wave output of its timer chip  36 . The AM signal was radiated to two receiving antennas  30  that were each connected to their own mixer  52 , 54 . A local oscillator input for both mixers  52 , 54  was created by multiplying a stable radio frequency reference from the signal generator  32   a  of the transceiver  32 . The mixers  52 , 54  subtracted the local oscillation frequency from the received signal frequency. The two resulting radio frequency signals were sent to a receiver  32   b  of the transceiver  32 . The receiver essentially did the same frequency down conversion operation over again. This time its from the radio frequency range to the audio (20 Hz to 20 kHz) range. The only difference was that its local oscillator frequency was adjustable so that the resulting audio signals could be tuned to fall into the “frequency window” generated by a low pass filter. The presence of the AM signal was detected visually with the spectrum analyzer  58  and the audio amplifier  60 . 
   Verification of the operation of the transponder  28  was successfully completed using the above. Presence of the AM signal&#39;s upper and lower side band odd harmonics were verified out to the 9 th  harmonic. Adjusting the receiver&#39;s local oscillating frequency made the spectrum of the AM signal slide back and forth in the frequency domain. When one of the AM signal&#39;s spectrum components fell into the low pass filter&#39;s frequency window, a sharp spike could be observed on the spectrum analyzer  58  and an audible tone could be heard from the audio amplifier  60 . When the transponder&#39;s 9V battery  40  was disconnected, the spike and tone would disappear except for the case when the carrier was tuned in. The spike and tone did not vanish in this case because the carrier was still being received directly from the signal generator. Turning the signal generator off verified this. It should be appreciated that the results of this test also showed that the transponder  28  is capable of using amplitude modulation by a radio frequency square wave pulse waveform. 
   Referring to  FIG. 5 , another embodiment, according to the present invention, of the transponder-based microwave telemetry apparatus  10  diagrammatically shown. Like parts have like reference numerals increased by one hundred (100). In this embodiment of the transponder-based microwave telemetry apparatus  110 , the transceiver  132  has a signal generator  180  to transmit a signal of 1.5 to 26 gigahertz (GHz), and a receiver to receive a signal of a frequency of about 144 megahertz (MHz) and to output a signal of about 1.0 KHz. The transceiver  132  may include a mixer  182  for the radio frequency signal. The mixer  180  can receive a radio frequency signal of about 1.5 to about 26 GHz. The transceiver  132  may include a filter  184  for receiving an input from the signal generator and for filtering the received signal. The transceiver  132  may include a frequency-to-voltage converter  186  having an output of the sensed condition and receiving an input from the filter  184 . It should be appreciated that the operation of the transponder-based microwave telemetry apparatus  110  is similar to the transponder-based microwave telemetry apparatus  10 . 
   The present invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. 
   Many modifications and variations of the present invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the present invention may be practiced other than as specifically described.