Abstract:
The presence of particulate debris flowing in a hydraulic fluid flow system includes a source of infra-red light passing through a window of the fluid flow line while fluid is flowing therethrough. A portion of the light is directed to a monitoring photodiode prior to reaching the fluid flow line. A detector photodiode is positioned to receive light passing through the flow line, the hydraulic fluid flowing therethrough and out of a second window. A trap is positioned between the hydraulic fluid flow line and the detector photodiode to prevent the direct rays of light from reaching the detector photodiode while permitting scattered light to reach the detector photodiode. A reduction in the amount of light reaching the detector photodiode results in an alarm being activated.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on Provisional Patent Application Serial No. 60/072,985 filed Jan. 20, 1998. 
    
    
     The present invention is directed to a method and apparatus for detecting suspension of particulate debris in hydraulic fluid systems. More specifically, the invention is directed to a device and method for both detecting the presence of such particles and monitoring an increase in the quantity or density of such particles while the hydraulic fluid is flowing through a hydraulic or other fluid flow line. The invention is particularly useful in that it can be mounted directly on a vehicle, industrial equipment including mobile equipment or specialized power machinery. 
     Under the present invention, a fluid specification monitor (FSM) is mounted to optically view and monitor the hydraulic fluid as it flows through a fluid flow line of the hydraulic system for example, in the hydraulic return line. The monitor can physically fit into the hydraulic fluid flow line. Under one embodiment, the portion of the fluid flow line being monitored can have the same flow area as the adjacent portions of the fluid flow line so that it will not create an added pressure drop to the system. 
     In one embodiment, a light emitting diode directs a beam of light through an aperture and then through a beam splitter, so that a sample of the axial light source can be taken by a monitoring photodiode to ascertain the amount of light being emitted by the diode source. The rest of the light is directed along the axial path through the liquid which is flowing as a small column through the fluid flow line. The fluid flow line is provided with windows of glass or a synthetic sapphire material which permit the light beam to pass through the fluid flow line and the hydraulic fluid flowing therethrough. On the opposite side of the fluid flow line is at least one collection lens. A light trap or mask is provided along an axis defined by the light emitting diode and the center of the collection lens in order to block any in-line light directly from the source. The light trap or mask is confined to the central portion of the collection lens lying within a small radius of the in-line axis so that scattered light radially outwardly of the mask will pass through the lens or lenses and will direct the light to a photodiode and amplifier electrically connected thereto. Particles, water and air bubbles, and other contaminants in the fluid will reflect and scatter part of the in-line light beam and this scattered light is to be detected optically. If the contamination level in the hydraulic fluid increases beyond a predetermined level, the photodiode will cause the electrical signal emitted by the amplifier to increase. Upon an increase beyond a predetermined amount, the monitor will set off an alarm to thereby permit the operator to take corrective action before the system is damaged. 
     The monitoring system of the present invention is not intended to detect or count individual particles but rather indicates the relative amount of light scattered from an aggregate amount of material moving through the oil chamber, as the light passes through the hydraulic fluid flowing through such oil chamber (i.e., a section of the fluid flow line). It is preferred that the monitoring system have digital electronics rather than analog electronics as a digital monitoring system is better able to process the optical signal and to compensate for variations in temperature of the infra-red light emitting diode and photodiode. Although analog circuitry is difficult to compensate for such variations in temperature, it is suitable for many applications. 
    
    
     REFERRING TO THE DRAWINGS 
     FIG. 1 is an opto-electronic block diagram for the monitor of the present invention. 
     FIG. 2 is an opto-electronic block diagram of another embodiment. 
     FIG. 3 is an enlarged fragmentary view of the optical portion of yet another embodiment. 
     FIG. 4 is a schematic diagram of the circuitry for the digital electronics for the embodiment of FIG.  1 . 
     FIG. 5 is a schematic diagram of the circuitry for the analog electronics for the embodiment of FIG.  2 . 
     FIG. 6 is an optical diagram showing a further embodiment. 
     FIG. 7 is an optical diagram showing yet another embodiment. 
    
    
     DETAILED DESCRIPTION 
     The opto-electronic block diagram and schematic diagram with the analog circuit is shown in FIGS. 2 and 5 and with the digital circuit is shown in FIGS. 1 and 4. FIG. 3 shows another embodiment in which the portion of the tube being monitored has a smaller diameter than the other portions of the fluid flow line. 
     The embodiments are similar in that they use optical and electronic components to determine the quality or condition of a working fluid such as hydraulic oil in order to send out an alarm when the fluid is contaminated. The assembly diagrams show both configurations. They both use an infra-red light emitting diode source to send a strong light beam straight through the oil flowing through a fluid flow line to detect particles or contaminants in the oil. 
     If the main light beam (axial) hits any particles, bubbles or material, these elements scatter some of the light in many directions. An optical trap is aligned on the main axis of the light, on the opposite side of the oil chamber from the light source. The trap blocks the direct light coming from the source, and prevents it from hitting the optical photodiode detector. This axial beam “light trap” is critical to the sensitivity of this equipment. 
     Some of the scattered light redirected away from the main axis is collected by a lens and directed toward a light sensitive photodiode at the end of the path. This photodiode detects the scattered light signal and in turn gives an electrical signal that is used to send an output alarm about the condition of the oil if the contaminants in the oil increase beyond a predetermined level as measured by the amount of light reaching the detector photodiode. In the embodiment of FIGS. 2 and 5, the photodiode amplifier will send the signal directly to the signal processor which relays it to the alarm. In the embodiment of FIGS. 1 and 4, the photodiode amplifier will send the signal to an analog-to-digital converter which relays it to a microcomputer which relays it to the alarm. 
     Under one embodiment, the source of light is monitored by another photodiode and an electrical feedback control “loop” for the purpose of holding the light level (amplitude) constant. In this way, the reference light level passed through the oil chamber or “viewing volume”, can be well controlled. However, it is also possible to utilize an infra-red light emitting diode which has a self-contained internal monitor for maintaining the light level constant thereby eliminating the need for an external monitoring photodiode or a beam splitter. 
     The differences in the digital and analog electrical circuit diagrams have to do mainly in the way the electrical signals are processed. The use of digital integrated circuits to process the signal voltages makes it easier to do temperature compensation of the electro-optic signal voltages than is possible with the analog circuits thereby improving the accuracy of the alarm signal over the high temperature operating conditions in which hydraulic equipment is used. 
     Referring to the drawings, FIGS. 1 and 4 show the fluid specification monitor (FSM)  10  with digital electronics with FIG. 1 showing a block diagram for such digital version. An oil chamber  11 , such as a fluid flow line portion of a hydraulic return line directs the flow of hydraulic fluid H. As shown in FIG. 1, the hydraulic fluid H has contaminants such as particles P. The fluid flow line functioning as the oil chamber  11  has positioned therein a pair of windows  12 A and  12 B to permit viewing through the oil chamber  11  and to permit the transmission through the oil chamber  11  and the hydraulic fluid H passing therethrough of a beam of infra-red light from an infra-red light emitting diode  14 . Positioned between the infra-red light emitting diode  14  and the oil chamber  11  is a lens  16  and a beam splitter  18 . A portion of the light passing through the beam splitter  18 , preferably about 70%, passes through the closest window  12 A thereto, through the hydraulic fluid H and exits from the opposing window  12 B along a path which is generally perpendicular to the flow of hydraulic fluid H through the oil chamber  11 . Preferably an opaque shield  17  having an aperture  17 A is mounted on or adjacent to the surface of the window  12 A facing the infra-red light emitting diode  14 . The shield  17  limits the amount of undesirable reflected light which may enter the chamber  11  and is effective in preventing false readings erroneously indicating the presence of excessive particles. As an example, if the window  12 A has a diameter of one-half inch, the size of the aperture  17 A will be 0.30 inch in diameter. For some applications, it may be desirable to have a plurality of shields with their respective apertures aligned along the alignment path. The other portion of the light reflected off of the beam splitter  18  is directed first to a monitoring photodiode  20  and then as an electrical current to a photodiode amplifier  22  and from there as a voltage to an analog-to-digital converter  24 . 
     A light trap or mask  26  is positioned to receive light from the infra-red light emitting diode  14  as it exits the window  12 B on the opposite side of the oil chamber  11  from the infra-red light emitting diode  14 . The infra-red light may have a peak wave length of 880 nanometers. However, this could vary and the light could be other than infra-red. The trap  26  is aligned with the infra-red light emitting diode  14 , the lens  16  and the windows  12 A and  12 B and has a size which will trap and block the light coming directly along such alignment path but will permit scattered light to pass therearound. The light trap has a diameter of about 4 millimeter (mm) and preferably is no larger than 5 mm in diameter. 
     Spaced from the light trap  26  is a lens  28  which receives the scattered light and focuses it on a detector photodiode  30 . Preferably, the lens has a diameter of about 21 mm with a possible range in the size of the diameter of 18 to 30 mm. Light from the detector photodiode  30  is transmitted to a photodiode amplifier  32  which transmits the scattered light voltage to the analog-to-digital converter  24 . 
     A feature of the digital embodiment of FIGS. 1 and 4 which is not present in the analog embodiment of FIGS. 2 and 5 is the presence of a thermally responsive resistor  34  which transmits information regarding temperature of the electrical and optical components, such as the infra-red light emitting diode  14  and photodiodes  20  and  30 , to the analog-to-digital converter  24  for forwarding to a microcomputer  46  which calculates and compensates for variations in temperature. The analog-to-digital converter  24  also transmits to the microcomputer  46  information regarding the scattered light voltage received from the photodiode amplifier  32  and information regarding the monitored voltage received from the photodiode amplifier  22 . If the microcomputer  46  computations indicate a high signal level as a result of contaminants viewed in the oil chamber  11 , it will alert an output alarm signal transistor  38 . 
     With additional reference to FIG. 4 along with FIG. 1, a +12 volt DC input voltage  42  from the vehicle or mobile equipment electrical system to which the monitor is mounted, goes into integrated circuit voltage regulator  44 . The voltage regulator  44  provides a regulated +5 volts for the circuitry of the FSM  10 . The voltage regulator  44  may be a National Semiconductor LM2937-5.0 or equivalent. The microcomputer  46 , which provides the digital control, computation and logic for the system, may be a Microchip PIC 16C622 8 bit microcomputer or equivalent. The microcomputer  46  has a 4 megahertz oscillator using an external resonator circuit  48 . This can be a 4.0 megahertz Murata ceramic resonator or a quartz crystal and two 22 picofarad ceramic capacitors. The output alarm signal transistor  38  (a MOSFET device such as 2N7000) is controlled directly from an output line from the microcomputer  46 . 
     A bidirectional serial data interface integrated circuit  52  is provided and functions as a charge pump to generate +9 &amp; −8 volts supply for the photodiode amplifiers  22  and  32 . One example of the integrated circuit  52  is Maxim MAX232A. The use of the bidirectional serial data interface integrated circuit  52  internal charge pump assists in extending the power supply regulator  44 . The amplifiers  22  and  32  may each be part of a dual operational amplifier such as Linear Technology LT1413. 
     An electrically erasable memory  54  such as a Microchip 93C66 or equivalent provides memory for the microcomputer  46 . The circuit also includes a dual digital-to-analog converter  25  such as a Linear Technology LTC1446. The microcomputer  46  sends two digital numbers to the dual digital-to-analog converter  25  which generates two separate analog voltages. One of these is needed as the control signal for a current driver  58  for the infra-red light emitting diode  14 . The other voltage controls an output voltage buffer amplifier  62  which provides an output voltage signal  60 . Another amplifier  64  functions as part of the constant current driver  58  for the infra-red light emitting diode  14 . Amplifiers  62  and  64  may each be part of a dual operational amplifier such as Linear Technology LT1413. A transistor  66 , driven by the amplifier  64 , controls the high current output to the infra-red light emitting diode  14 . The transistor  66  is a 2N5582 or equivalent. 
     The photodiode  30  for scattered light detection and the monitored light photodiode  20  from the beam splitter  18  are connected to amplifiers  32  and  22 , respectively. These amplifiers  32  and  22  convert the photodiode currents into voltage signals which, along with several other voltage signals, are measured by the analog-to-digital converter  24  that converts multiple channels of input voltages to an output digital number, one channel at a time, and then transmits such output digital number to the microcomputer  46 . 
     This system operates as follows: The microcomputer  46  takes a fixed value from memory microchip  54  and sends it to the dual digital-to-analog converter  25  where it is converted to a voltage output to the amplifier  64  and the output voltage buffer amplifier  62 . The output current drives the infra-red light emitting diode  14  to generate the light source. The monitoring photodiode  20  measures this light and is read by the analog-to-digital converter  24 . The microcomputer  46  compares the reading and controls the infra-red light emitting diode  14  current and light level. Scattered light detected by the photodiode  30  is read the same way by the analog-to-digital converter  24  and the microcomputer  46 . A high signal level from the detector photodiode  30  indicates excessive contamination and results in an output alarm being sent from the microcomputer  46  to the alarm output signal  38 . Two other voltages are read by the analog-to-digital converter  24  for temperature compensation. One is the voltage directly across the infra-red light emitting diode  14 , which is related to the internal diode temperature. The other one is from a thermistor  34 , a thermally responsive resistor, whose voltage and temperature can be read by the analog-to-digital converter  24  and the microcomputer  46 . Temperature compensation is done by calculation inside the microcomputer  46  using the data read by the circuit and adjustments are made electronically. 
     Referring to FIGS. 2 and 5, there is shown a fluid specification monitor (FSM)  50  with analog electronics. In FIG. 2 there is shown a block diagram for the analog version of the FSM  50 . An oil chamber  11 , such as a fluid flow line portion of a hydraulic return line directs the flow of hydraulic fluid H. As shown in FIG. 2, the hydraulic fluid H has contaminants such as particles P. The fluid flow line functioning as the oil chamber  11  has positioned therein a pair of windows  12 A and  12 B to permit viewing through the oil chamber  11  and to permit the transmission through the oil chamber  11  and the hydraulic fluid H passing therethrough of a beam of infra-red light from an infra-red light emitting diode  14 . Positioned between the infra-red light emitting diode  14  and the oil chamber  11  is a lens  16  and a beam splitter  18 . A portion of the light passing through the beam splitter passes through the closest window  12 A thereto, through the hydraulic fluid H and exits from the opposing window  12 B along a path which is generally perpendicular to the flow of hydraulic fluid H through the oil chamber  11 . The other portion of the light exiting the beam splitter  18  is directed first to a monitoring photodiode  20  and then to a photodiode amplifier  83  and from there to a light source level control  84  which functions to insure that the amount of light being emitted from the infra-red light emitting diode  14  is constant. 
     A light trap or mask  26  is positioned to receive light from the infra-red light emitting diode  14  as it exits the window  12 B on the opposite side of the oil chamber  11  from the infra-red light emitting diode  14 . The trap  26  is aligned with the infra-red light emitting diode  14 , the lens  16 , the beam splitter  18  and the windows  12 A and  12 B and has a size which will trap and block the light coming directly along such alignment path but will permit scattered light to pass therearound. 
     Spaced from the light trap  26  is a lens  28  which receives the scattered light and focuses it on a detector photodiode  30 . The sizes of the trap  26  and lens  28  are similar to those of the embodiment of FIGS. 1 and 4. Light from the detector photodiode  30  is transmitted to a photodiode amplifier  72 . The photodiode amplifier  72  transmits the scattered light voltage to a signal processor  51 . If the scattered light voltage reaches a level indicating excessive contamination of the hydraulic fluid H, the signal processor  51  will cause the alarm signal  53  to be activated. 
     With specific reference to FIG. 5, an integrated circuit (IC) voltage regulator  144  takes direct current (DC) input voltage of 12 volts and provides a regulated +5 volt output for the electronic circuitry. The voltage regulator  144  could be an IC device such as Power Trends 78SR105HC. The input voltage comes in through connector  70  on pin # 1 , with pin # 2  serving as the ground return. The DC voltage/power supply components are shown on the schematic of FIG. 5 but not on the block diagram of FIG.  2 . 
     An output driver transistor  90  delivers current to the infra-red light emitting diode  14  through pin # 1  of connector  71  to which the infra-red light emitting diode  14  is connected. 
     Alarm output signals  138  and  139  are connected through pins # 4  and # 5  of the connector  70  and come from transistor switches  74  and  75 . These transistor switches  74  and  75  are equivalent to BUZ 11  MOSFET types. The signals for the transistor switches  74  and  75  are received through junction block  76  which in turn receives the signals from the outputs of a semiconductor driver array  78  that switches on a sequence of ten output lines  79 A- 79 J when the input voltage increases. This semiconductor driver array  78  may be National Semiconductor LM3914. These 10output lines  79 A- 79 J activate a sequence of 10 output alarm indicators consisting of linear array of visible colored light emitting diodes,  53 A through  53 J. The first four indicators or light emitting diodes,  53 A through  53 D, are green indicating “Low/OKAY”, the next three indicators,  53 E through  53 G are yellow indicating “Medium/Caution”, and the last three indicators,  53 H through  53 J are red indicating “High/Alarm”. 
     The signal input voltage into the semiconductor switch  78  that causes the output indicators to light comes from the two stage amplifier noise filter/integrator circuit. The first stage is the photodiode amplifier  72 , which generates an output voltage signal from an input current from the scattered light detector photodiode  30  which is connected electrically through connector  71 , pin  5  and to ground on pin  6 . The second stage is a signal integrator and noise filter amplifier  73  giving a slow output signal response from a rapidly changing input. Both amplifiers  72  and  73 , can be National Semiconductor type LF347, for example. These IC amplifiers are powered by DC voltages from charge pump  77  which generates +10 and −10 volts from the +5 volt regulated supply. The charge pump  77  may be a Linear Technology Part LT1054, for example. Also, a voltage reference device  87  provides a precision reference voltage of +2.5 volts for the circuit and is a Maxim type MAX873. 
     The light source feedback control loop begins at pin # 3  of the connector  71 . The monitoring photodiode  20  sends an input signal through pin # 3  of connector  71  to an amplifier  81 . The amplifier  81  sends a DC voltage to another amplifier  82  which changes the polarity of the input signal from negative to positive. A third amplifier  83  provides voltage gain for the light monitor signal sent by the monitoring photodiode  20 . All three amplifiers  81 ,  82  and  83  are of a type such as National Semiconductor LF347. The third amplifier  83  also compares the signal voltage to a reference voltage input from an adjustable resistor  85 , and reverses the output voltage from positive to negative. Resistor  85  setting creates the reference voltage of around +2.5 volts for the light source level. 
     In the operation of the control loop, a lower level of light emitted, as detected by the monitoring diode  20 , results in lower output voltage from the first and second amplifiers  81  and  82 . At the third amplifier  83 , the lower input level is compared to the constant reference level, and detects a drop in voltage. The output then increases substantially due to the gain of the amplifier. This increasing output voltage is connected directly into the output driver transistor  90  input. The resulting increased drive current from the output driver transistor  90  goes to the infra-red light emitting diode  14  and corrects for the low light level detected by the monitor, thus completing the operation of the control loop. As previously mentioned, if the scattered light reaching the detector photodiode  30  from the lens  28  is reduced such that the amount of voltage transmitted from the photodiode amplifier  72  to the signal processor  51  indicates excessive contamination of the hydraulic fluid H (i.e. excessive particles P), the signal processor will cause the alarm output  53  to be activated. 
     Referring to FIG. 3, the fluid specification monitoring system is shown in use with a fluid flow line section  111 . In this embodiment, the fluid flow line section  111  extends along an axis A from a first end  112  to a second end  113  and has inwardly facing threads  114  adjacent each of said first end  112  and said second end  113 . As shown in phantom lines, a tubular section  115  having an internal diameter D is engaged to the threads  114  at the second end  113 . Another tubular section (not shown) is engaged to the threads  114  at the first end  112 . 
     The fluid flow line section  111  has a constricted area  120  having a diameter which is smaller than the internal diameter D of the tubular sections  115 . A pair of windows  121  are mounted in the constricted area  120  on opposite sides of the axis A and aligned such that the beam of infra-red light emitted from the infra-red light emitting diode  14  passes through each of the windows  121 . 
     The embodiments of FIGS. 1,  4  and  2 ,  5  both utilize a beam splitter  18  and a monitoring photodiode  20  for insuring against faulty readings activating the alarm signal due to variations in the amount of light emitted by the infra-red light emitting diode  14 . Preferably by maintaining the intensity of the light at a constant level, it is also possible to utilize the broad concept of the present invention without using a beam splitter  18 . 
     Under one embodiment, this is accomplished by utilizing a self-monitoring light emitting diode, for example, one manufactured by Integrated Photomatrix Inc., Hillard, Ohio under its Part No. IPL 10630. 
     Under another embodiment, as shown in FIG. 6, the elimination of the beam splitter  18  is accomplished by positioning the monitoring photodiode  20  in a location where it can capture light from the infra-red light emitting diode  14  which is reflected off of the window  12 A. This is shown in FIG. 6 which shows the monitoring photodiode  20  positioned adjacent to the infra-red light emitting diode  14 . As shown in dashed lines, the light from the infra-red light emitting diode  14  exiting the lens  16  includes a divergent beam portion B 1  which, after striking the surface of the window  12 A at an angle to the line of alignment L of the infra-red light emitting diode  14  and the light trap  26  is reflected back as a reflected beam portion B 2  which is read by the monitoring photodiode  20 . 
     FIG. 6 also shows a preferred system of lenses. As in the embodiment of FIG. 1, a lens  16  is positioned between the infra-red light emitting diode  14  and the window  12 A, being much closer to the diode  14  than to the window  12 A. The shield  17 , having an aperture  17 A, is mounted on or closely adjacent to the receiving surface of the window  12 A in order to restrict to the greatest extent possible the light source entering the window  12 A to that which is emitted by the infra-red light emitting diode  14 . On the opposite side of the chamber  11 , spaced from the window  12 B, is a first double convex lens  27 . A second double convex lens  29  is positioned between the first double convex lens  27  and the detector photodiode  30 . The light trap  26  is positioned between the two double convex lenses  27  and  29  but much closer to the second double convex lens  29  or even in contact with the surface thereof. 
     The first double convex lens  27  receives light exiting the window  12 B and focuses it onto the light trap  26  with any scattered light resulting from contamination by particles P reaching the second double convex lens  29  which focuses such scattered light to the detector photodiode  30 . 
     FIG. 7 shows a further preferred embodiment which utilizes double convex lenses  27  and  29  as in the embodiment of FIG. 6 but which utilizes a beam splitter  18  for directing the split beam to the monitoring photodiode  20 . 
     The size and cross-sectional size and configuration of that portion of the monitoring device containing the windows and the hydraulic fluid to be monitored (i.e. the view chamber) may be varied depending upon the flow rate, pipe diameter and optic performance. For example, it is within contemplation of the present invention that the viewing chamber containing the windows have a rectangular as well as circular or other cross-sectional configuration. Additionally, for some applications it may be desirable that the cross-sectional size of such viewing chamber be larger that the size of the pipes directing the flow of liquid therethrough. 
     In addition to the embodiments discussed above, it will be clear to persons skilled in the art that numerous modifications and changes can be made to the above invention without departing from its intended spirit and scope.