Patent Application
20160041024
A transducer is a device that converts energy from one form (e.g., electrical) to another (e.g., mechanical). Transducers are used in a variety of automotive, commercial, and industrial applications. Ceramic crystals are used as transducers in ultrasonic devices or sensors. The crystals convert an electrical input into sound waves. Ultrasonic devices can use the piezoelectric effect to measure changes in pressure, acceleration, strain or force by converting these changes to an electrical charge. Ultrasonic devices (e.g., ultrasonic sensors or piezoelectric transducers) can be used in various applications, such as medical imaging, non-destructive testing, or distance and level sensing applications.
In ultrasonic level sensing as used with a tank of fluid, a typical level sensor is designed and built as a self-contained unit and assembled through an opening in the wall of a tank or combined with some other component, such as a fuel module, which is also assembled through an opening in the wall of the tank. Other typical level sensors may be self-contained units and assembled within the tank. Depending on the type of level sensor, the level sensor is either immersed within the fluid or resides in the airspace located directly above the fluid.
Embodiments of the invention relate to an ultrasonic sensor formed by a tank (e.g., automotive fuel tank) coupled to an ultrasonic sensor subassembly. Various systems and methods are described for coupling (e.g., bonding) the tank to the ultrasonic sensor subassembly, testing the coupling of the tank to the ultrasonic sensor subassembly and the ultrasonic sensor, and programming the ultrasonic sensor for a specified tank design and type of fluid being measured.
In one embodiment, the invention provides ultrasonic sensor subassembly configured to form an ultrasonic sensor upon coupling to a tank having a tank wall. The ultrasonic sensor subassembly includes a sensor subassembly housing, a planar piezoelectric element located within the sensor subassembly housing, and circuitry electrically connected to the planar piezoelectric element. The planar piezoelectric element includes a surface configured to couple to the tank wall such that the tank wall forms a matching layer of the ultrasonic sensor. The circuitry is configured to produce a signal to drive the planar piezoelectric element to generate a sound wave and receive an indication of a detected echo from the planar piezoelectric element.
The surface of the planar piezoelectric element can be coupled or bonded to the tank wall using an adhesive. The tank can be configured for a motorized vehicle or equipment, such as a motor vehicle (e.g., motorcycles, cars, automobiles, trucks, buses, trains), watercraft (ship or boat), aircraft, or spacecraft. The tank can be used to contain various types of fluids, such as fuel, gasoline, diesel, oil, coolant, diesel exhaust fluid (DEF), brake fluid, transmission fluid, windshield washer fluid, water (e.g., fresh water, gray water, or black water), or any other fluid needing a continuous level measurement. The ultrasonic sensor and tank can be well suited to high volume production used in motorized vehicles and equipment.
The circuitry of the ultrasonic sensor subassembly can include a printed circuit board (PCB) or a system on chip (SoC). The circuitry can be configured to test or verify the coupling between the tank wall and the planar piezoelectric element of the ultrasonic sensor. The circuitry can also be configured to extrapolate a fluid level for a specified tank design and a type of fluid being measured or determine a concentration of the fluid using a strapping table that maps an output (e.g., a detected echo of a sound wave) from the ultrasonic sensor against a predefined table of values. The circuitry and sensor can provide a level indication proportional to the volume of fluid remaining within the tank or an actual level measurement depending on the original equipment manufacturer (OEM) implementation. The ultrasonic sensor can be configured to measure a fluid concentration or a fluid level.
The ultrasonic sensor subassembly can also include a temperature sensor electrically connected to the circuitry configured to detect a temperature of a fluid in the tank. The temperature of the fluid sensed by the temperature sensor can be an input to the strapping table to extrapolate a fluid level for a specified tank design and a type of fluid being measured or determine a concentration of the fluid. For example, a processor can use the temperature values and time of flight values as the variables for strapping a table and generate a fluid level either as a volume of fluid remaining or an actual level measurement. The ultrasonic sensor subassembly can include an integral connector or a wire harness electrically coupled to the circuitry to provide a connector or interface to an external computing device (e.g., a testing device or a programming device) for testing the ultrasonic sensor or programming the circuitry. The testing device can be configured to test the ultrasonic sensor formed by a combination of the ultrasonic sensor subassembly and the tank wall. The programming device can be configured to program the circuitry of the ultrasonic sensor subassembly with a strapping table that maps an output from the time of flight measurement from the ultrasonic sensor and temperature against a predefined table of values to extrapolate a fluid level for a specified tank design and/or a type of fluid being measured.
The ultrasonic sensor subassembly can include various other components. For example, the planar piezoelectric element can have a matching layer on both planar surfaces. The matching layers (e.g., a first matching layer) can be used to match an acoustical impedance of the planar piezoelectric element to the tank wall. Thus, a second matching layer can be coupled to a surface of the planar piezoelectric element opposite the surface that is configured to be coupled to the tank wall, where the tank wall provides a first matching layer. The ultrasonic sensor subassembly can also include leads electrically coupling each planar surface of the planar piezoelectric element to the circuitry, and a piezo potting material to support the leads or movement of the planar piezoelectric element in the sensor subassembly housing. A cover can be used to protect the circuitry and the planar piezoelectric element of the ultrasonic sensor subassembly from external environmental conditions, and a printed circuit board (PCB) potting material can be used to support or protect the circuitry and other components in the ultrasonic sensor subassembly.
In another embodiment, the invention provides a tank coupled to an ultrasonic sensor subassembly. The tank has a tank wall configured to be coupled to the ultrasonic sensor subassembly. An ultrasonic sensor is formed by the coupling of the ultrasonic sensor subassembly with the tank wall of the tank. The ultrasonic sensor subassembly includes a sensor subassembly housing, a planar piezoelectric element located within the sensor subassembly housing, and circuitry electrically connected to the planar piezoelectric element. The planar piezoelectric element includes a surface coupled to a tank wall such that the tank wall forms a matching layer of the ultrasonic sensor. The circuitry is configured to produce a signal to drive the planar piezoelectric element to generate a sound wave and receive an indication of a detected echo from the planar piezoelectric element. The detected echo is the sound wave that is reflected off the surface of the fluid within the tank.
The tank wall forms a sensor subassembly receptacle to mate with the sensor subassembly housing and aligns the tank wall with the surface of the planar piezoelectric element. The sensor subassembly receptacle can include a mechanism to fasten the sensor subassembly housing to the tank. For example, the fastener can include a snapping mechanism, a clasp, a latch, or other attachment mechanism, where the sensor subassembly receptacle and the sensor subassembly housing have corresponding mating features. The fastener can be used to hold the sensor subassembly housing in position against the tank wall during bonding or curing of the adhesive. The tank can include stiffeners (e.g., stiffening ribs on a perimeter of the sensor subassembly receptacle) to provide a rigid structure for the sensor subassembly receptacle.
The tank wall can include features to enhance the coupling, bond, or bond line between the tank wall and the planar piezoelectric element of the ultrasonic sensor subassembly. For example, the tank wall can be configured to pass ultrasonic energy and include at least three spacers defining a uniform planar surface of the matching layer. The spacers can be configured to maintain a substantially uniform bond line between the planar piezoelectric element and the tank wall. For instance, each spacer can have columnar, pyramidal, or dome-like shape. The substantially uniform bond line can have a substantially constant thickness controlled by a height of the spacers. In one example, the spacers can form a grid and define grid openings for receiving an adhesive for the substantially uniform bond line.
A focus tube can be integrally formed by the tank or included within the tank. A focus tube or measuring tube can extend from a lower wall section of the tank upwards towards an upper wall section of the tank to improve detection of a correct fluid level by the ultrasonic transducer. The height of the focus tube can be dictated by the angle performance requirements of the specific application. For example, the height of the focus tube may not extend all the way to the upper wall and may form a structural element within the tank that is substantially shorter than the distance from the lower wall section of the tank to the upper wall section of the tank. The planar piezoelectric element can be coupled to a surface of the tank wall that is on an opposite side of the tank wall to an area within the focus tube. A plane or a surface formed by an upper end of the focus tube is nonparallel (e.g., angled) with respect to the fluid plane to reduce interference from signals bouncing off the plane or the surface formed by an upper end of the focus tube. The plane formed by an upper end of the focus tube may be open or closed. A focus tube float can be confined by the focus tube to improve reflection of a sound wave generated by the ultrasonic sensor.
In another embodiment the invention provides a method of bonding an ultrasonic sensor subassembly to a tank wall of a tank to form an ultrasonic sensor. The method can include providing the tank, which can be formed using a variety of process, such as blow molding, rotational molding, rotary or roto molding, or injection molding. The method can further include cleaning (e.g., plasma cleaning) a bond line surface of the tank wall or cleaning (e.g., plasma cleaning) the surface of the planar piezoelectric element, where the bond line is the interface between the tank wall and the planar piezoelectric element. The bond line surface of the tank wall can include spacers to provide a substantially constant thickness of the bond line. The can be formed during fabrication of the tank.
The method can further include applying an adhesive to the tank wall or a surface of a planar piezoelectric element located within the sensor subassembly. Then, coupling the surface of the planar piezoelectric element of the ultrasonic sensor subassembly to the tank wall in an area with the adhesive (i.e., bond line) to form an ultrasonic sensor such that the tank wall forms a matching layer of the ultrasonic sensor. The method can further include curing the adhesive (e.g., a polymer) to toughen or harden the adhesive.
The method can provide for testing the ultrasonic sensor to verify a bond between the tank wall and the surface of the planar piezoelectric element. For example, the testing can include coupling the ultrasonic sensor subassembly to a testing device via an integral connector. The testing device can stimulate the ultrasonic sensor to measure the ring time at multiple power levels by sending a message to the ultrasonic sensor for the ultrasonic sensor to enter a self-test mode. Once in the self-test mode the ultrasonic sensor measures the ring time at various power levels and communicates the resulting information to the testing device. The measured ring time responses can be compared against specified threshold values in an acceptance table for a specified tank design to verify that the ring time responses of the ultrasonic sensor fall within the specified threshold values indicating a functioning ultrasonic sensor for the specified tank design. Under damped ring times (i.e., ring times that are too long) or over damped ring times (i.e., ring times that are too short) can cause an ultrasonic sensor to fail a self-test. For example, testing the ultrasonic sensor can be performed without any fluid within the tank. Fluid in the tank can dampen the signals used for testing and shorten expected ring time values, which can reduce the resolution of the measured signals and the testing device's capability to discern good ultrasonic sensors from bad ultrasonic sensors.
The method can provide for programming the circuitry of the ultrasonic sensor subassembly with a strapping table that maps an output from the ultrasonic sensor against a predefined table of values. The strapping table along with the output from the ultrasonic sensor can be used to extrapolate a fluid level for a specified tank design and a type of fluid being measured or extrapolate a fluid concentration. For example, the strapping table can map a type of the fluid, a time of flight as measured from a detected echo return signal, and a temperature of the fluid to create an output value representative of a volume of the fluid or a depth of the fluid remaining within the tank. The planar piezoelectric element, matching layers, a piezo potting material, a tank material, a tank wall thickness, a bond line material, bond line dimensions can be factors in the development of an ultrasonic transducer that can efficiently transmit energy up into the fluid.
Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. The same reference numerals in different drawings represent the same element. Numbers provided in flow charts and processes are provided for clarity in illustrating steps and operations and do not necessarily indicate a particular order or sequence. As used herein the term “or” can refer to a choice of alternatives (e.g., an exclusive or) or a combination of the alternatives (e.g., and/or).
Embodiments of the invention relate to an ultrasonic sensor formed by a tank coupled to an ultrasonic sensor subassembly. For example, as illustrated in
Unless otherwise indicated, the phrases “ultrasonic sensor,” “ultrasonic transducer,” “piezoelectric sensor,” “piezoelectric transducer,” “sensor,” and “transducer,” may be used interchangeably to refer to an ultrasonic sensor 116. Unless otherwise indicated, the phrases “ultrasonic sensor subassembly,” “sensor subassembly,” and “subassembly” may be used interchangeably to refer to an ultrasonic sensor subassembly 120. Unless otherwise indicated, the phrases “ultrasonic sensing system” and “sensing system” may be used interchangeably to refer to an ultrasonic sensing system including the tank, ultrasonic sensor subassembly, and the ultrasonic sensor formed by the tank and ultrasonic sensor subassembly. Unless otherwise indicated, the phrases “piezoelectric element,” “planar piezoelectric element,” or “piezo layer” may be used interchangeably to refer to a piezoelectric element 130. Planar piezoelectric element 130 refers to a configuration of the piezoelectric element allowing a surface to be coupled to a tank 100 and not the orientation of the piezoelectric element relative to the tank. The planar piezoelectric element 130 can be configured in a horizontal orientation, vertical orientation, or some other orientation to the tank 100.
Unlike typical ultrasonic sensors, the ultrasonic sensing system described herein relies on the tank 100 having been constructed with features enabling the attachment of the sensor subassembly 120 and controlling the piezo bond line 118 to insure that the combination of the bond line adhesive, tank material, and dimensions of the assembly create an ultrasonic transducer 116 that is both efficient and will resonate at the natural frequency of the selected piezoelectric material and configuration. The sensor subassembly 120 can include circuitry that allows customization of the sensing system, post assembly (i.e., after assembly), to facilitate different tank sizes, shapes, and application fluids. The circuitry can include hardware, firmware, program code, executable code, computer instructions, and/or software. In addition the sensor subassembly can include self-test circuitry to measure and broadcast application specific measurement data that enables an external test machine or device to evaluate whether the sensing system is operating as intended following assembly into the tank.
The ultrasonic sensing system described herein provides various benefits over typical ultrasonic sensors. For example, typical level sensors are designed and built as a self-contained unit for a specific tank design and assembled through an opening in the wall of a tank or combined with some other component, such as a fuel module, which is in turn assembled through an opening in the wall of the tank. Depending on the technology selected, the level sensor is either immersed within the fluid, resides in the airspace located directly above the fluid or both. Several disadvantages are associated with the typical ultrasonic sensor within the tank. For instance, the typical ultrasonic sensor has to be uniquely designed and calibrated for each different tank design into which the sensor is being assembled, which can create a proliferation of different parts, different part numbers, assembly processes that can increase costs. The typical ultrasonic sensor within a tank is either exposed to the fluid or fluid vapors, which can be corrosive to the sensor that can create challenges with reliability and increased cost depending on the fluid being measured. In addition, the tank for a typical ultrasonic sensor has to have an opening in one of the tank walls from which to assemble the sensor or larger module including the sensor. The opening can create a potential leak path for the fluid or vapor emissions. In the case of an automotive gasoline tank in the United States (US), evaporative emissions is regulated by the Environmental Protection Agency (EPA) resulting in an increased governmental standards and regulations to insure that the resulting tank designs are leak tight. Other countries may have similar governmental or administrative agencies (similar to the EPA in the US) to regulate fluid or vapor emissions and protect the environment.
Alternatively, a self-contained ultrasonic sensor may be arranged on the outside of the tank using a semisolid contact material (e.g., grease or ultrasonic gel), an elastomer, or an adhesive. These through wall ultrasonic sensors can use point level devices attached to the side of the tank visa via the contact material, elastomer, or adhesive. In these through wall sensor applications, the self-contained sensors are calibrated after being assembled to the tank to identify the ultrasonic signature difference when fluid is present or not in the tank on the opposite side of the tank wall opposing the point level sensor. The calibration of these self-contained sensors on the tank wall requires that the tank to be filled with fluid. These point level devices can detect a discrete state of the fluid, such as empty or possibly full, but unfortunately these point level devices do not have the sensitivity or granularity to detect a continuous level reading from a full tank condition to an empty tank condition.
For example, a self-contained ultrasonic sensor is attached outside of the tank (e.g., to the bottom of a tank) with contact material (e.g., ultrasonic gel) between the self-contained ultrasonic sensor and the tank wall. The gel allows at least a portion of the sound energy to be passed through the tank wall, but the tank wall is not part of the resonant system. Ultrasonic gels are commonly available for making ultrasound scans.
In another ultrasonic sensor configuration, the housing features of an ultrasonic sensor 116 (e.g., a level sensor) can be replicated in the wall 102 of a tank 110. Then, the components of the ultrasonic sensor 116, such PCB 140, piezoelectric material or plate 130, piezo potting 138, PCB potting 144, connector 124, 126, and 128, terminals and the like, can be assembled into the wall 102 of the tank 100 where the tank 100 is used as the primary substrate or housing for the ultrasonic sensor 116. Unfortunately, the processes and equipment for manufacturing and assembling the ultrasonic sensor 116 differ from the processes and equipment for molding and assembling the tank 100. The assembly of the individual components of the ultrasonic sensor into the wall of a tank can require equipment and technical expertise not typically used by tank manufacturers. The assembly of the individual components of the ultrasonic sensor 116 into the wall 102 of a tank 100 may be used in a one off or low volume production environment, but may not be economical or logistically feasibly for large volumes, such as scenarios where different tank designs are manufactured at various locations in the world by those skilled in molding and assembling tanks and ultrasonic sensors are manufactured in another location in the world by those skilled in assembling ultrasonic sensors. Conversely, creating a sensor manufacturing process uniquely tailored for each tank molding site can require too much investment per unit of production due to the diversity of tank designs and relatively low volumes produced for each tank design.
Another challenge with this approach of assembling the individual components of the ultrasonic sensor 116 into the wall 102 of a tank 100 is that the tank wall thickness, which is a function of the process being employed, may not be particularly well controlled (e.g., have large tolerances). The tank wall thickness may vary generating changes in the functionality of the sensor 116, which can produce erroneous readings in the fluid levels (or fluid concentrations).
The ultrasonic sensing system described herein overcomes many of these challenges associated with in-tank ultrasonic sensors, self-contained ultrasonic sensors arranged outside the wall of the tank, and the assembling of the individual components of the ultrasonic sensor into the wall of a tank. In an embodiment, the ultrasonic sensing system described applies a common ultrasonic sensor design that can be deployed across multiple tank designs 100A (
The ultrasonic sensing system described herein can have various features. For example, the ultrasonic sensing system creates a resonant ultrasonic transducer where the tank wall 120 forms an integral part of the transducer 116 once the sensor subassembly 120 is affixed to the tank 100. The sensor subassembly 120 may be attached to the tank 100 in such a way that the complete ultrasonic sensing system can be assembled on site at a tank molder's manufacturing facility with the minimum of equipment, tooling, and technical known how. The ultrasonic sensor design can be created independent of a tank's shape or the fluid selected for the tank 100. Following assembly of the ultrasonic sensor 116, the ultrasonic sensor can be customized or programmed for a particular tank shape and fluid contained by the tank 100. Because the ultrasonic sensor 116 can be assembled at a facility other than the site used to manufacture the ultrasonic sensor subassembly 120, the ultrasonic sensor 116 can perform a self-test function to determine whether the ultrasonic sensor 116 functions correctly indicating that the sensing system was assembled and cured correctly.
As illustrated in
The piezo layer 130 may have various orientations relative to the circuitry (e.g., PCB 140) or the ultrasonic sensor subassembly. For example, the surface of the piezo layer 130 configured to couple with the tank wall 102 may be oriented in parallel with a plane of the circuitry (e.g., PCB 140) of the ultrasonic sensor subassembly 120, as illustrated in
Referring back to components of the ultrasonic sensor subassembly 120, the temperature sensor 142 (e.g., a thermistor or a thermometer) determines a temperature or a temperature gradient of the subassembly using technologies known in the art. The temperature sensor 142 can be used to determine the temperature of the fluid, which can be used to adjust data generated by the sensor 116.
For example, the temperature of the fluid can be used to correct for a change in the speed of sound, which occurs with changing temperatures. The temperature then becomes an input into a strapping table along with a time of flight (TOF) of a detected echo return signal. The values within the strapping table can be set up during calibration to represent a desired output for a tank size shape and fluid being measured for each specific temperature and time of flight combination. Circuitry and/or software can provide a linear interpolation between strapping table values (e.g., temperature and TOF values) to reduce a size of the strapping table.
As shown in
In another embodiment, a wireless component or device coupled to the circuitry may be used to configure and test the sensor 116 using a wireless protocol. The wireless component or device may be powered by a battery or other energy storage device included in the sensor subassembly circuitry, or the wireless component or device can provide two-way communication between the circuitry and the testing device or programming device. The wireless protocol used by the wireless component or device can include any short range or long range wireless protocol, such as the third generation partnership project (3GPP) long term evolution (LTE), the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard (e.g., 802.16e, 802.16m), which is commonly known to industry groups as WiMAX (Worldwide interoperability for Microwave Access), the IEEE 802.11 standard, which is commonly known to industry groups as Wi-Fi, or Bluetooth. Including the wireless component or device to the sensor subassembly 120 can add cost to the sensor subassembly 120 due to the radio features or energy storage device, but can be used in some applications.
An aspect of an ultrasonic measurement system design that greatly influences the performance of the sensor 116 is the selection of the resonant frequency for operating the ultrasonic sensor 116. Resonance is the tendency of a sensor or system to oscillate with greater amplitude at some frequencies than at others. The materials, thickness, and shape used for the piezo layer 130 and the matching layers 102 and 136 can change the resonant properties of the ultrasonic transducer 116. A first layer matching layer is formed by the tank wall 102 and a second matching layer 136 is present in the subassembly 120. Typical ultrasonic sensor designs start with a piezo layer of a particular thickness and diameter, which in turn dictates a specific operating frequency depending on which mode the piezo layer is vibrating in. Thickness or radial vibration modes are common types of vibration modes for the piezo layer. Once the thickness and diameter of a piezo layer is selected in a typical ultrasonic sensor design, the tank wall thickness between the piezo layer and outside world is selected along with a bond line to create a system that resonates at the selected frequency of operation and maximizes the transmission of ultrasonic energy through the tank wall into the fluid being measured. The bond line 118 is the interface coupling the tank wall 102 to the piezo layer 130 and contributes to the frequency characteristics of the sensor 116. The bond line 118 or 342 (
The ultrasonic sensor 116 described herein separates the sensor subassembly manufacture from the sensor wall fabrication, specifically as the sensor wall fabrication relates to tank wall 102 and tank molding. For instance, the wall thickness of the tank 100 is a function of the tank design and the process employed to construct the tank 100 (e.g., injection molding, blow molding, rotational molding, and similar processes). The bond line dimensions, piezo layer selection, and the matching layer designs are developed around a nominal tank wall thickness rather than finely controlling the tank wall thickness during the tank manufacturing process. An advantage of designing the sensor 116 around the nominal tank wall thickness is that the ultrasonic sensor design accommodates the method of producing the tank 100 rather than changing the method of producing the tank 100 or forcing the tank's production method to yield a result that may not be attainable (e.g., producing tank walls with smaller or tighter tolerances). Thus a common sensor subassembly 120 can be manufactured efficiently in high volume and applied across multiple tank designs significantly reducing manufacturing cost when the method of tank production (e.g., rotary molding or blow molding) is similar across a wide variety of tank sizes and shapes, as illustrated in
Although
In another configuration, the piezo layer 130 (
The tank design may include additional features to accommodate the sensor subassembly 120. For example, the section of the tank wall that is configured to be coupled to the sensor subassembly 120 can include features to improve the uniformity of the bond line thickness, as shown and described in U.S. Pat. No. 7,176,602 to Schlenke, entitled “Method and Device for Ensuring Transducer Bond Line Thickness,” with a patent date of Feb. 13, 2007, which is herein incorporated by reference in its entirety. Excessive adhesive or bond thickness can adversely affect the characteristics of a transducer or sensor, which can include changing the angle of the piezo layer 130 relative to the tank wall 102. In some applications, the optimum thickness of the adhesive is 0.002″-0.005″. The optimum thickness is based on the specific transducer-to-housing interface 118 (e.g., piezoelectric layer-to-tank wall interface) or bond line 342 (
The bond line features on the tank wall 102 can be manufactured or etched by the tank manufacturer. The tank manufacturer can also apply the adhesive to the bond line 118 and couple the tank wall 102 with the bond line features to the piezo layer 130 of the sensor subassembly 120 to form an integrated through wall ultrasonic sensor 116.
Referring back to
The tank design may also include other additional features to accommodate the sensor subassembly 120. For example, the tank 100 can include a sensor subassembly receptacle formed within the tank wall 120, where the sensor subassembly receptacle includes features that mate with the sensor subassembly. The sensor subassembly receptacle or tank wall 102 in the tank 100 can include features to provide a rigid structure for the sensor subassembly or rigidity in the area surrounding the sensing system (i.e., sensor subassembly 120), such as thicker tank walls 104, stiffing ribs 106, or similar features. The additional rigidity serves to reduce the stress being applied to the bond line 118 and sensor subassembly attachment features when the tank 100 is subjected to extreme overpressure or shock events.
Another feature of the tank design is a physical means by which the sensor subassembly 120 is held in the correct position while the bond line adhesive fully cures. Once the bond line adhesive is cured the physical means provides rigidity to the entire sensor 116 and tank structure 110, which can minimize the stress being applied to the bond line during changes in temperature and vibrational loads. The physical means can include a fastener, such a snapping mechanism 108, a clasp, a latch, threaded mechanism, or other attachment mechanism. Any suitable attachment method can be used as long as the method holds the sensor 116 in place against the features defining the bond line 118.
The tank 100 may include a focus tube 110 or measuring tube that is integrally formed with the tank 100 or inserted into tank 100 during the tank manufacturing process. The focus tube 110 can extend from one wall section of the tank toward another wall section of the tank to improve detection of a correct fluid level or fluid concentration by the ultrasonic sensor 116. In another embodiment, the focus tube 110 may only extend a portion of the height of the tank 100. The focus tube 110 may be used depending on the application and the specific sensor use regarding level measurement at various incident angles. For example, if the tank 100 is to subject to moderate angles, such as 6° to 15°, during operation then the focus tube 110 can improve the ultrasonic sensor's capability to determine a fluid level. The focus tube 110 can include at least one vent 162, such as a vent at the bottom portion of the focus tube 110, to allow fluid to flow in and out of the focus tube 110 from the tank 100. The vent 162 to allows the fluid within the focus tube 110 to self-level match the fluid that within the remainder of the tank 110 by either filling the focus tube 110 when the height of the fluid level of the tank 100 is above the fluid level of the focus tube 110 or draining the fluid in the focus tube 110 when the height of the fluid level of the tank 100 is below the fluid level of the focus tube 110.
A top portion of the focus tube 110 can include an angled surface 160 to reduce interference due to ultrasonic signals bouncing off the surface of the focus tube 110, which interference can prevent accurate sensing of the surface of the fluid being measured. Reflected sound waves can bounce off a top surface of the focus tube 110 if top surface of the focus tube 110 is parallel to the fluid surface. The reflection off the top parallel surface of the focus tube 110, which includes an ultrasonic signal traveling back up to the surface of the fluid and returning back down the focus tube 110, creates interference by canceling out the ultrasonic signal reflected off the surface of the fluid, particularly at low fluid levels when the ultrasonic sensor 116 is operating in a near field mode, as described and taught by U.S. Pat. No. 6,573,732 to Reimer, entitled “Dynamic Range Sensor and Method of Detecting Near Field Echo Signals,” with a patent date of Jun. 3, 2003, which is herein incorporated by reference in its entirety. The cancellation effect due to a reflection of a focus tube surface can be referred to as echo cancellation. An angled focus tube surface or an angled focus tube mitigates echo cancellation by causing the sound waves to bounce off at angles different from the primary sound waves used in level sensing, which disperses the energy elsewhere within the tank so the reflected energy has minimal effect to a level sensing measurement. Although, an angled surface to the focus tube 110 is shown, other configurations, such as a rounded, saw tooth, or castle shape, may also be used to disperse or deflect any sound waves reflecting off of the top of the focus tube 110.
In another configuration, a focus tube can extend upwards near the top of the tank 100. In another example, a focus tube can extend upwards to the top of the tank 100 with a float specifically designed to reflect ultrasonic signals may be used in off highway vehicles where operation at 45 degree incident angles can occur. The focus tube 110 can be molded into the interior of the tank 100, 100A, and 100B or the focus tube 110 can be inserted into the tank as a separate component through an existing opening or as a feature built into a fuel module, as shown and described in U.S. Pat. No. 8,302,472 to Rumpf, entitled “Fuel Delivery Unit with a Filling Level Sensor Operating with Ultrasonic Waves,” with a patent date of Nov. 6, 2012, which is herein incorporated by reference in its entirety.
The ultrasonic sensing system and ultrasonic sensor fabrication process described herein can begin with an existing tank molding process used to fabricate tanks. The variability of the tank wall thickness of the wall 102 of a tank 100 can change the resonant characteristics of the ultrasonic sensor 116. For example, the ultrasonic sensor 116 including a tank 100 with a thicker or thinner tank wall from a nominal tank design may still resonant but the ring time response may be over damped. The ultrasonic sensor 116 (with thicker or thinner walls) having the over damped ring time response can utilize more energy than a ultrasonic sensor with a tank wall having a nominal designed thickness in order to generate and receive an ultrasound echo that is reliable under extremes of temperature, inclination angle, and vibration. The calibration and programming of the ultrasonic sensor 116 can be used to compensate for the variably of the tank wall used to form the ultrasonic sensor 116.
Since the ultrasonic sensing system including both the tank 100 and sensor subassembly 120 is independent of tank shape or fluid application, the output of sensor 116 has to be corrected for the tank design or fluid application using a strapping table that maps the raw sensor data against a predefined table of values to extrapolate fluid level for the particular tank shape and fluid being measured. The raw sensor data can include temperature corrected time of flight (TOF) data generated by the round trip emission, reflection, and detection of the ultrasonic wave. For example, the strapping table can include an X-Y table, where the size is dependent on a desired resolution. One axis can represent temperature and another axis can represent timer values or counts representative of the time of flight, as measured by the microcontroller. For instance, the temperature axis may have steps with 7.81 C increments ranging from −40 C to 85 C and the time of flight axis may have steps with 31.25 microsecond (μsec) increments ranging from 0 to 1000 μsecs. For this example, the result is a 512 element table capable of operating over an expected range of temperatures and fuel measurements for tanks up to 500 mm deep. The table axes may use binary representations of the equivalent values of temperature or TOF (e.g., a microcontroller internal timer) as measured by an analog to digital (A/D) converter instead of temperature values in degrees C. or time values in μsecs. Each table elements can be populated with a digital representation of an expected output for that specific temperature and time of flight. A microcontroller can then use the conditioned time of flight and temperature to find the bordering table values from which the microcontroller then performs a two axis interpolation function to arrive at a correct output value.
The strapping table can be customized for the tank design and the fluid to be measured in the tank. The strapping table can be loaded into a module external (e.g., local fuel system controller or an electronic control unit (ECU) for a fuel tank) to the tank 100 in applications where a strapping module exist and is separate from the sensor subassembly 120, or the strapping table can be loaded or downloaded into the circuitry of sensor subassembly (e.g., microcontroller) prior to or following assembly into the tank 100. When the strapping table is loaded or downloaded into the circuitry of the sensor subassembly 120, an output operating mode can be included in the circuitry allowing serial communication of the sensor data through an electrical connector (e.g., integral connector) regardless of the type of sensor output desired.
For example, a user may desire a simple resistive output emulation, which can be selected by the strapping table data, where the sensor changes the load current and voltage at the electrical connector terminals in proportion to the measured level, which can be a normal mode of operation of the ultrasonic sensor 116. In a first operating mode (e.g., normal operating mode), the sensor measures the level of the fluid and performs basic diagnostic functions to insure that the sensor is providing correct measurement information. A second operating mode can include a fault mode of operation where the sensor 116 detects an issue with the returned echo quality, temperature measurement, or some other internal function and can then provide an output indicative of the fault that was detected. Other operating modes (e.g., self-test, programming, and calibration operating modes) can use the same electrical connector terminals as a serial bi-directional data link through which an external computer can be used to program a strapping table into the sensor subassembly circuitry and provide means by which the circuitry can communicate diagnostic data to facilitate a self-test sequence. For example, a third mode of operation can include an initial self-test sequence occurring following assembly of the sensor subassembly 120 into the tank 100. In this self-test mode of operation, the sensor 116 measures the ring-time of the piezo element at various power levels within a dry tank. These measurements can be uploaded to an external host computer and/or test station and based on the measurements the host computer determines if the results were acceptable or not acceptable for that particular tank 100, which can be used as part of quality control to reject tanks 100 improperly bonded with the sensor subassembly 120. The fourth mode of operation can include the calibration mode where the host computer downloads the strapping table values as determined for the specific tank, size, shape, fluid type, and output desired. The third and fourth modes of operation may include a disabling or lockout mechanism, which may be activated by the host computer, to prevent the sensor 116 from being changed after self-testing, programming, or calibration, such as when the tank assembly leaves the factory.
A similar process can be used for ultrasonic sensors designed with a pulse-width modulation (PWM) output, voltage output, current loop, and any serial data outputs, such as single edge nibble transmission (SENT) protocol, local interconnect network (LIN) protocol, controller area network (CAN) protocol, or another custom serial data protocols. PWM is a modulation technique that controls the width of the pulse (or pulse duration) based on modulator signal information. Society of Automotive Engineers (SAE) J2716 SENT is a point-to-point protocol for transmitting signal values from a sensor to a controller that allows for high resolution data transmission with a lower system cost than other serial data protocols. The SENT protocol is a one-way, asynchronous voltage interface which uses three wires: a signal line with a low state less than 0.5 volts (V) and a high state greater than 4.1V, an approximately 5V supply voltage line, and an approximately 0V ground line. For example in the SENT protocol, data are transmitted in units of 4 bits (1 nibble) and a SENT message is 32 bits long (8 nibbles) and includes 24 bits of signal data (6 nibbles) that represents 2 measurement channels of 3 nibbles each (such as pressure and temperature), 4 bits (1 nibble) for cyclic redundancy check (CRC) error detection, and 4 bits (1 nibble) of status/communication information. SENT is a low cost solution that can convey measurement information as well as diagnostic information. CAN is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer. The CAN protocol uses a two-wire bus priority based scheme. LIN is a serial network protocol used for communication between components in vehicles. The LIN protocol uses a one-wire daisy-chain or bus with a shunt master-slave topology.
In another embodiment, the strapping table data is programmed into the sensor subassembly circuitry via the wireless component or device or diagnostic data from the sensor subassembly circuitry is obtained via the wireless component or device.
Since the coupling or bonding of the sensor subassembly 120 to the tank wall 102 can be performed at a facility (e.g., tank molding facility) different from the facility manufacturing the sensor subassembly, the sensor subassembly 120 can include features and programming to provide self-testing of the assembled ultrasonic sensor 116 (including the tank wall 102). The assembled ultrasonic sensor 116 can be tested for a particular type of fluid, even without filling the tank 100 with that fluid. Testing the sensor by filling the tank with a quantity of fluid and then comparing the output to the specified value can be very time consuming, difficult, and possibly dangerous depending on the particular fluid in a production environment. Self-testing of the ultrasonic sensor 116 can avoid these challenges. Self-testing can compare dry tank values that correspond to acceptable values for a particular type of fluid and tank design, which can be generated using a prototype of the tank design and the fluid used. As a result of the self-testing functionality, the tank molding operation where sensor subassemblies 120 are assembled to the tank 100 may not have to have the ultrasonic sensor knowhow on site to help diagnose complex problems, maintain sensitive processes, or evaluate whether the sensor is working correctly. The sensor subassembly circuitry via a testing device can verify that the ultrasonic sensor 116 is functioning correctly for the specific application, tank, or fluid. The sensor 116 can perform a self-test following assembly into the tank 100, which can occur in close succession to the time during which the strapping table is being programmed into the sensor 116. By combining these two activities (e.g., self-testing and programming), the sensor 116 can have a cable plugged into the electrical connector (e.g., integral connector 124, 126, and 128) a single time for both testing and programming, which can save assembly time and labor, thus reducing the cost of assembling the ultrasonic sensor 116.
An ultrasonic sensor 116 as a resonant system has a certain ring time response dependent on the applied energy used to stimulate the piezo layer 130. Self-testing maps the ring time response of the sensor 116 when assembled into the tank 100 that exposed to ambient conditions (e.g., room temp and air) at one or more power levels. The time that the sensor 116 takes for the piezo layer 130 to stop ringing at a particular power level is proportional to the quality factor (Q, Q factor, or Quality) of the resonant acoustic circuit. The quality factor is a dimensionless parameter that describes damping an oscillator or resonator or equivalently characterizes a resonator's bandwidth relative to the resonator's center frequency. A higher Q indicates a lower rate of energy loss relative to the stored energy of the resonator, where the oscillations die out more slowly. Measuring these ring time values at various power levels can provide a reasonably accurate picture of how well the transducer 116 is functioning within the tank 100 without having to fill the tank with fluid.
The sensor subassembly 120 when entering into the self-test mode of operation can measure the ring time at one or more power levels and broadcast the ring time though the serial bi-directional data link (via the electrical connector) to an external test and programming device (e.g., computer). The external computer can then compare the measured ring times against an acceptance table uniquely derived for the particular tank integration. The acceptance table can include threshold ring time values indicating proper functionality of the ultrasonic sensor for a particular tank and fluid. In an embodiment, the acceptance table can be stored on the external computer in conjunction with the strapping table for a specific tank design. Each unique tank design can have a differing resonant profile. By storing the expected resonant profile for a particular tank design on an external test computer along with the strapping table can result in a sensor that is relatively independent of tank design, so a common and less costly ultrasonic sensor subassembly 120 can be broadly applied across multiple tank designs and assembled to a tank 100 by the tank manufacturer.
An adhesive can be selectively applied to the bond line surface of the tank 100, as in block 430. In other examples, the adhesive can be selectively applied to the bond line surface of the piezo layer 130. The sensor subassembly 120 can be aligned, coupled, or assembled to the tank 100 to form an ultrasonic sensor 116, as in block 440. The alignment can be provided by the matching or corresponding structures of the sensor subassembly 120 and sensor subassembly receptacle along with any fasteners 108 and 148. The fasteners can apply pressure on the piezo layer 130 against the tank wall 102 while the adhesive cures, as in block 450. The sensor subassembly circuitry performs a self-test via an external computer (e.g., testing computer) to verify the ultrasonic sensor functionality for the specific tank design and fluid to be used, as in block 460. The external computer (e.g., programming computer) can also program the sensor subassembly circuitry with a strapping table that can map raw sensor data to a usable fluid level or fluid concentration, as in block 470.
As can be shown in the flow chart of
Another example provides a method 500 for bonding an ultrasonic sensor subassembly to a tank wall of a tank to form an ultrasonic sensor, as shown in the flow chart in
As used herein, a plurality of items, structural elements, compositional elements, and/or materials may be presented in a common list for convenience. However, these lists should be construed as though each member of the list is individually identified as a separate and unique member. Thus, no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary. In addition, various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof. It is understood that such embodiments, examples, and alternatives are not to be construed as defacto equivalents of one another, but are to be considered as separate and autonomous representations of the present invention.
Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided, such as examples of layouts, distances, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention can be practiced without one or more of the specific details, or with other methods, components, layouts, etc. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention.
While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.
