Abstract:
A fluid condition and level sensor is provided that includes a solenoid body, a coil, and an armature surrounded by the coil. The solenoid body defines an armature chamber in which the armature is movable in response to energizing of the coil. The sensor is mounted to a reservoir such that a first portion of the solenoid body extends into a cavity defined by the reservoir, and so that movement of the armature is substantially transverse to a direction of fluid level change in the reservoir. The first portion of the solenoid body defines an opening permitting fluid communication between the cavity and the armature chamber, such that fluid enters and is displaced from the armature chamber through the opening as the armature moves, movement of the armature within the armature chamber thereby being affected by fluid level in the reservoir.

Description:
TECHNICAL FIELD 
     The present invention relates to fluid level sensors, such as an oil level sensor in an automotive engine. 
     BACKGROUND OF THE INVENTION 
     Monitoring fluid levels is important in a wide variety of systems and mechanisms. For example, in many fluid systems, fluid level in a reservoir achieves a static level when the fluid is not in use, and a dynamic level lower than the static level when in use, such as when it is cycled through a system by a pump. Maintaining appropriate static and dynamic levels may be important to system efficiency and function. In one such system, an automotive engine, regular oil changes are necessary for proper maintenance. An oil level sensor may be incorporated into the vehicle to alert the driver when oil needs to be added. 
     SUMMARY OF THE INVENTION 
     A fluid condition and level sensor is provided that includes a solenoid body and a coil within the solenoid body. An armature is surrounded by the coil. The solenoid body defines an armature chamber in which the armature is movable in response to energizing of the coil. In a fluid condition and level sensing system, the coil is operatively connected to a controller which can determine at least one of fluid temperature, fluid viscosity, fluid level, and a fluid change occurrence. The sensor may be mounted to a fluid-containing reservoir such that a first portion of the solenoid body extends into a cavity defined by the reservoir. The sensor may be positioned so that movement of the armature is substantially transverse to a direction of fluid level change in the reservoir. The first portion of the solenoid body within the cavity defines an opening permitting fluid communication between the cavity and the armature chamber, such that movement of the armature within the armature chamber is affected by fluid level in the reservoir. 
     The sensor may be referred to as an integrated fluid condition and level sensor as multiple sensing functions may be integrated into one sensor. The sensor may be used in many different applications where there is a need to measure fluid level, fluid viscosity and/or fluid temperature, such as in engines, transmissions, differentials, food processing, stationary press oil gear boxes, and fluid cooling systems. 
     In some embodiments, the solenoid body defines a second opening, with the first and second openings arranged to permit fluid communication between fluid in the reservoir and the armature chamber at respective opposing sides of the armature and at different levels within the reservoir. Travel time of the armature in the armature chamber corresponds to the resistance to fluid flow through the openings. The “fluid flow” through each respective opening may be air, a liquid, such as oil, or a combination of both, and depends upon the fluid level (i.e., liquid level) in the reservoir. 
     For example, if liquid level is low, air, rather than liquid, will be drawn into the armature chamber. Because air flows much more freely than liquid, the average armature travel time, also referred to as response time, will be shorter when liquid level is low. Thus, the “fluid flow” within the chamber and through the openings discussed herein may be either air or a liquid, depending on liquid level in the reservoir. 
     The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic cross-sectional illustration of a first embodiment of an a fluid condition and level sensing system including an fluid condition and level sensor mounted to a fluid-containing reservoir shown in fragmentary cross-sectional view; 
         FIG. 2  is a schematic cross-sectional illustration of a second embodiment of a fluid condition and level sensing system including a fluid condition and level sensor; and 
         FIG. 3  is a schematic perspective illustration in exploded view of the fluid condition and level sensor of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein like reference numbers refer to like components,  FIG. 1  shows a fluid condition and level sensing system  10  including a fluid condition and level sensor  12  extending through a side wall  14  of a fluid reservoir  15 . The fluid reservoir  15  may be an oil pan in an engine, or a transmission, may be a differential, a food processing container, or any fluid reservoir. The sensor  12  is secured to the reservoir  15 , such as an engine oil pan on a vehicle, so that the fluid condition and level sensor  12  is positioned in the reservoir  15  to enable detection of multiple fluid conditions, including fluid temperature, fluid viscosity, a full fluid level, and a low fluid level, as further described herein. The fluid condition and level sensor  12  is operatively connected to an electronic controller  16 , which may be contained either inside or outside of the reservoir  15 , such as on a vehicle engine or elsewhere in the vehicle. 
     Referring to  FIG. 1 , the fluid condition and level sensor  12  has a solenoid body  20  that includes an outer portion  22 , also referred to as a can, a base portion  24 , a coil support portion  26 , an extension portion  28  and a cap portion  34 . The coil support portion  26  (also referred to as a bobbin) supports a coil  30 . The outer portion  22 , base portion  24 , coil support portion  26 , extension portion  28 , and cap portion  34  may be made integral or made unitary with one another by casting, molding, or other processes. 
     A pole piece  32  is press-fit or otherwise secured within the outer portion  22 . The cap portion  34  surrounds a distal end of the pole piece  32  and has an electrical connector  36  therethrough operatively connected to a power source  38 , such as a battery, and to the controller  16 . Flux collectors  40  are positioned between the pole piece  32  and the cap portion  34 . 
     The base portion  24  and extension portion  28  of the solenoid body  20 , along with the pole piece  32 , define an armature chamber  42  in which an armature  44  travels between an end surface  46  of the base portion  24  and an end surface  48  of the pole piece  32 . The armature  44  includes a body portion  50  and a rod portion  52  extending therefrom. A biasing device, such as spring  53 , is positioned between the pole piece  32  and the armature body portion  50  to bias the armature  44  away from the pole piece  32  to the unenergized position shown (i.e., the position of the armature  44  when the coil  30  is not energized). 
     A mounting flange  51  secures the sensor  12  through an opening  54  in the reservoir side wall  14 . A bolt or other fastening mechanism (not shown) extends through mating openings  56 ,  58  of the flange  51  and the side wall  14 . When secured to the reservoir  15 , the base portion  24  extends into a cavity  60  defined by the reservoir  15 . The remainder of the sensor  12  is external to the reservoir  15 . The base portion  24  has an upper opening  62  and a lower opening  64 . As used herein, upper opening  62  is referred to as the first opening. 
     The armature  44  travels generally transverse to a direction of fluid level change in the reservoir  15 . That is, the armature  44  travels back and forth in the armature chamber  42  generally transverse (perpendicular) to the direction of decreasing fluid level (from level A, to level B, to level C, to level D), or increasing fluid level (from level D, to level C, to level B, and to level A). The sensor  12  may alternatively be mounted so that the armature travels at a different angle with respect to fluid in the reservoir  15 . 
     The pole piece  32 , outer portion  22 , coil  30 , flux collectors  40 , flange  51  and armature  44  form an electromagnet. Lines of flux are created in a gap  66  between the pole piece  32  and the armature  44  when the coil  30  is energized by the electric source  38 . When the coil  30  is energized, the magnetic flux drives the armature  44  toward the pole piece  32 , decreasing the portion of the armature chamber  42  between end surface  48  and the armature  44 . When energy to the coil  30  ceases, the spring  53  drives the armature  44  back to the unenergized position shown, increasing the portion of the armature chamber  44  between surface  48  and armature  44 . Fluid, whether air or liquid, is pushed through the openings  62 ,  64  as the armature  44  travels. Fluid in the gap  66  of the armature chamber  42  is also forced through a clearance  67  between the outer diameter of the armature  44  and the inner diameter of the extension portion  28  as the armature  44  is cycled. Fluid is similarly forced through channels  69  in the armature  44 . The clearance  67  and channels  69  are configured to be more resistant to fluid flow than the openings  62 ,  64 . Thus, armature travel time is a function of the resistance to fluid flow through clearance  67  and channels  69 , which in turn is dependent on whether air or liquid is present in the chamber  42  and forced through the clearance  67  and channels  69 . 
     The solenoid valve  20  has a distinctive inductive kick, which is a distinct dip in current draw followed by an increase in current draw indicative of the armature  44  reaching the end of travel under known fluid temperature and fluid fill level. The time period to an inductive kick after the solenoid valve  20  is energized, is thereby affected by the resistance to travel encountered by the armature  44 . 
     The chamber  42 , clearance  67 , channels  69 , and openings  62 ,  64  described above establish armature travel times indicative of various fluid conditions such as fluid viscosity and a fluid change occurrence, as well as various fluid levels in the reservoir  15 , as described below. By tracking the time until inductive kick, and comparing the time with predetermined times in a look-up table stored on the controller  16 , the controller  16  is able to determine liquid level and viscosity. The sensor  12  is also operable to determine oil temperature based on current. 
     Fluid Viscosity 
     When the coil  30  is energized and deenergized, the armature  44  moves within the chamber  42 . When the armature  44  moves away from the pole piece  32 , fluid is also pushed through clearance  67  and channels  69  from chamber  42 . By summing the total resistance to fluid flow through the clearance  67  and channels  69  and friction of the moving parts, this slows the armature movement such that by measuring the time of armature motion and then applying an algorithm stored in controller  16 , the response time corresponds to a value indicating the viscosity of the fluid. A higher fluid viscosity causes the armature  44  to move more slowly as it is cycled, increasing the armature response time. The inductive “kick” that occurs at the end of the armature travel in the cycle is detected by the controller  16 , which is connected to coil  30 . The thicker the fluid, the longer it will take for the inductive kick to occur. The total armature response time is then checked in a look-up table stored in the controller  16  to obtain the relative viscosity of the fluid. Fluid viscosity can thus be measured using the sensor  12 , except when liquid fluid level is at an extreme low level (i.e., below opening  64 , such as at level D). 
     The resistance of the sensor  12  may also be measured and the engine controller voltage controlled to maintain a constant operating current to the sensor  12  and thus a constant force of the armature  44 . This reduces any effects of current variability on the armature response time. Limiting the voltage below 12 volts can slow the armature  44  even further to modify the response time versus viscosity relationship and thereby increase the sensor sensitivity. 
     Fluid Level 
     When liquid fluid within the reservoir  15  is above a predetermined full level B, such as at level A, armature travel time is a function of the sum of the resistances to fluid travel through the clearance  67  and the channels  69 , with viscous drag on the armature  44  also having a slight effect. The openings  62 ,  64  are sized large enough to permit fluid flow therethrough relatively freely, so that flow through the clearance  67  and channels  69  determines armature travel time. Because these resistances will vary as liquid fluid level varies, the fluid condition system  10  can monitor and record liquid fluid level within the reservoir  15 , recognizing the instant current liquid level as being within one of two ranges: above a first level (full level B), and below a second level (low level C. This information can be conveyed to a system operator, such as a vehicle driver, if desired, by connecting a display monitor, such as on an instrument panel screen, to the controller  16  and programming the controller  16  to send a display signal to the monitor corresponding to the monitored fluid level. 
     If liquid level in the pan  15  is at any level below the opening  64  (i.e., below level C), as indicated by “excessive low” fluid level D in  FIG. 1 , any fluid in the chamber  42  is forced out of openings  62 ,  64  on the first armature cycle. When the armature  44  cycles, air is drawn into the chamber  42  instead of liquid, since the openings  62 ,  64  are above the liquid level. On subsequent cycles, because only air is moving through the openings  62 ,  64 , clearance  67 , and channels  69 , the armature movement time is relatively fast. Thus, the controller  16  will recognize such an armature travel time as indicative of an “excessive low” liquid fluid level, will store this information, and may be programmed to send a notification to a display in order to notify the vehicle operator of the need to add fluid. 
     When liquid fluid is at any level above the opening  62  (i.e., above level B), the chamber  42  will be constantly filled with liquid as the armature  44  travels, and liquid will be forced through the clearance  67  and channels  69 . This will create a unique armature travel time recognized by the controller  16  as indicative of a full liquid fluid level, and being a function of the sum of resistances to fluid flow through clearance  67  and channels  69 . The sensor  12  may be mounted to the reservoir  15  such that level B represents a minimum desired static liquid level and level C represents a minimum desired dynamic liquid level. 
     Fluid Temperature 
     The temperature of the coil  30  will be affected by the fluid. To measure fluid temperature, the coil resistance is measured and then checked against a temperature look-up table stored within the controller to determine the temperature of the fluid. Alternatively, the sensor  12  may be cycled with a predefined voltage. By measuring the current, the coil resistance can be calculated and then correlated with temperature. 
     Second Embodiment 
     Referring to  FIG. 2 , another embodiment of a fluid condition and level sensing system  110  including a fluid condition and level sensor  112  extending through a side wall  114  of a reservoir  115 . The sensor  112  is secured the reservoir  115 , such as an engine oil pan on a vehicle, so that the fluid condition and level sensor  112  is positioned in the reservoir  115  to enable detection of multiple fluid conditions, including fluid temperature, fluid viscosity, and multiple fluid levels, as further described herein. The fluid condition and level sensor  112  is operatively connected to an electronic controller  116 , which may be contained either inside or outside of the reservoir  115 , such as on a vehicle engine or elsewhere in the vehicle. 
     Referring to  FIG. 2 , the fluid condition and level sensor  112  has a solenoid body  120  that includes an outer portion  122 , also referred to as a can, a base portion  124 , a coil support portion  126 , and a cap portion  134 . The coil support portion  126  (also referred to as a bobbin) supports a coil  130 . The outer portion  122 , base portion  124 , coil support portion  126 , and cap portion  134  may be made integral or made unitary with one another by casting, molding, or other processes. 
     A pole piece  132  is press-fit or otherwise secured within the outer portion  122 . The cap portion  134  surrounds a distal end of the pole piece  132  and has an electrical connector  136  therethrough operatively connected to a power source  138 , such as a battery, and to the controller  116 . Flux collectors  140  are positioned between the pole piece  132  and the cap portion  134 . A washer  141  is positioned between the coil support portion  126  and the base portion  124 . 
     The base portion  124  of the solenoid body  120 , along with the pole piece  132 , define an armature chamber  142  in which an armature  144  travels between an unenergized position shown (near an end surface  146  of the base portion  124 ) and an energized position (closer to an end surface  148  of the pole piece  132 ). A biasing device, such as spring  153 , is positioned between the pole piece  132  and the armature  144  to bias the armature  144  away from the pole piece  132  to the unenergized position shown (i.e., the position of the armature  144  when the coil  130  is not energized). 
     A mounting flange (not shown) secures the sensor  112  through an opening  154  in the reservoir side wall  114 . A bolt or other fastening mechanism (not shown) extends through mating openings of the flange and the side wall  114 . When secured to the reservoir  115 , the base portion  124  extends into a cavity  160  defined by the reservoir  115 . The remainder of the sensor  112  is external to the reservoir  115 . 
     The base portion  124  has an extension  161  with an upper opening  162  and a lower opening  164 . As used herein, upper opening  162  is referred to as the first opening. As best shown in  FIG. 3 , the lower opening  164  extends axially and is in communication with a radial slot  165 . 
     In this embodiment, the armature  144  travels generally transverse to a direction of fluid level change in the reservoir  115 . That is, the armature  144  travels back and forth in the armature chamber  142  generally transverse (perpendicular) to the direction of decreasing liquid fluid level from level AA, to level BB to level CC, to level DD, or increasing liquid fluid level change from level DD, to level CC, to level BB, and to level AA. The sensor may alternatively be positioned so that the armature travels at other angles with respect to the fluid level. 
     The pole piece  132 , outer portion  122 , coil  130 , flux collectors  140 , washer  141  and armature  144  form an electromagnet. Magnetic flux is created when the coil  130  is energized by the electric source  138 . The magnetic flux drives the armature  144  toward the pole piece  132 , increasing the portion of the armature chamber  142  between end surface  146  and the side  145  of the armature  144 . When energy to the coil  130  ceases, the spring  153  drives the armature  144  back to the unenergized position shown, decreasing the portion of the armature chamber  142  between surface  146  and armature  144 . Fluid, whether air or liquid, such as oil, is pushed through the openings  162 ,  164  as the armature  144  travels. Opening  162  communicates air or liquid with the chamber  142  at a first side  145  of the armature  144 . Opening  164  communicates air or liquid within the reservoir  115  below level DD with a second side  147  of the armature  144 . Air can be communicated between the portions of the chamber  142  at the two sides  145 ,  147  of the armature  144  through a clearance  166  between the inner diameter of the cavity forming the chamber  142 , and the outer diameter of the armature  144 . The clearance  166  is designed to inhibit any communication of liquid therethrough. Thus, armature travel time is a function of the resistance to fluid flow through the openings  162 ,  164 , which in turn is dependent on whether air or liquid is flowing through the openings. The time period to an inductive kick after the solenoid  112  is energized, is thereby affected by the resistance to fluid flow through the openings  162 ,  164 . The chamber  142  and openings  162 ,  164  described above establish armature travel times indicative of various fluid conditions such as fluid viscosity and a fluid change occurrence, as well as various fluid levels in the reservoir  115 , as described below. By tracking the time until inductive kick, and comparing the time with predetermined times in a look-up table stored on the controller  116 , the controller  116  is able to determine liquid fluid level and viscosity. The sensor  112  is also operable to determine fluid temperature based on current. 
     Fluid Viscosity 
     When the coil  130  is cycled (energized and deenergized), the armature  144  moves back and forth within the chamber  142 . When the coil  130  is energized and deenergized, the armature  144  moves toward and away from the pole piece  132 , respectively, and fluid is pushed through openings  162 ,  164  from chamber  142 . The total resistance to fluid flow of the openings  162 ,  164  and friction of the moving parts slows the armature movement such that by measuring the time of armature motion and then applying an algorithm stored in the controller  116 , the response time corresponds to a value indicating the viscosity of the fluid. A higher fluid viscosity causes the armature  144  to move more slowly as it is cycled, increasing the armature response time. The inductive “kick” that occurs at the end of the armature travel toward the pole piece  132  is detected by the controller  116 , which is connected to coil  130 . The thicker the fluid, the longer it will take for the inductive kick to occur. The total armature response time is then checked in a look-up table stored in the controller  116  to obtain the relative viscosity of the fluid. Fluid viscosity can thus be measured using the sensor  112  (except when fluid is at an extreme low level (i.e., below opening  164 , such as at level D)). 
     The resistance of the sensor  112  may also be measured and the engine controller voltage controlled to maintain a constant operating current to the sensor  112  and thus a constant force of the armature  144 . This reduces any effects of current variability on the armature response time. Limiting the voltage below 12 volts can slow the armature  144  even further to modify the response time versus viscosity relationship and thereby increase the sensor sensitivity. 
     Fluid Level 
     When liquid within the reservoir  115  is above a predetermined full level AA, armature travel time is a function of the sum of the resistances to fluid travel through each of the openings  162 ,  164 , with viscous drag on the armature  144  also having a slight effect. Because these resistances will vary as liquid fluid level varies, the fluid condition system  110  can monitor and record fluid level within the reservoir  115 , recognizing the current liquid fluid level as being within one of three ranges: above level AA (e.g., an overfill level), below level DD (e.g., a low level), and between level AA and level DD (e.g., a full level). This information can be conveyed to a vehicle operator, if desired, by connecting a display monitor, such as on an instrument panel screen, to the controller  116  and programming the controller  116  to send a display signal to the monitor corresponding to the monitored liquid fluid level. 
     If fluid level in the reservoir  115  is at any level below the opening  164 , (i.e., any level below level DD in  FIG. 1 ), any liquid fluid in the chamber  42  is forced out on the first armature cycle. When the armature  144  cycles, air is drawn into the chamber  42  instead of liquid, since the openings  162 ,  164  are above the liquid fluid level. On subsequent cycles, because only air is moving through the openings  162 ,  164 , the armature movement time is relatively fast. Thus, the controller  116  will recognize such an armature travel time as indicative of an “excessive low” liquid fluid level, will store this information, and may be programmed to send to a display a notification to the system operator of the need to add oil. 
     If liquid fluid level in the pan  115  is at any level below the opening  162 , but above the opening  164  (i.e., a level between level AA and level DD, such as level BB and level CC, the armature  144  will displace at least some liquid fluid out of the chamber  142  on the first armature cycle. When the spring  153  biases the armature  144 , opening  164  will draw in fluid. Because opening  162  is above the liquid fluid level, and at least some of the chamber  142  is above liquid fluid level, some air will be drawn into the chamber  142  when the sensor  112  is energized. Therefore, the armature movement time will be slower than when liquid fluid is at the extreme low level DD, but not as slow as when fluid level is above opening  162 . The controller  116  will compare the armature movement time to stored values and recognize such an armature travel time as indicative of a level between level AA and level DD. 
     When liquid fluid is at any level above the opening  162 , such as above level AA, the chamber  142  will be constantly filled with liquid fluid as the armature  144  travels, and liquid will be forced through openings  162 ,  164 . This will create a unique armature travel time recognized by the controller  16  such as indicative of an overfill level, depending on the mounted position of the sensor  112  within the reservoir  115 , and being a function of the sum of resistances to fluid flow through openings  162 ,  164 . 
     Fluid Temperature 
     The temperature of the coil  130  will be affected by the fluid. To measure fluid temperature, the coil resistance is measured and then checked against a temperature look-up table stored within the controller to determine the temperature of the fluid. Alternatively, the sensor  112  may be cycled with a predefined voltage. By measuring the current, the coil resistance can be calculated and then correlated with temperature. 
     While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.