Sensor system for passive in-vehicle breathing alcohol estimation

Abstract

A method for passive breathing alcohol detection, the method comprising: A) passively obtaining a first air sample from air within a vehicle interior; b) determining the concentration of (i) tracer gas and (ii) analyte present in the first air sample; c) passively obtaining a second air sample from the air within the interior of the vehicle; d) determining the concentration of (i) tracer gas and (ii) analyte present in the second air sample; e) continuing to passively obtain a number N of air samples from the air within the interior of the vehicle and, for each air sample obtained, determining the concentration of tracer gas and analyte present in the air sample; f) determining the number of peaks of the concentration of the tracer gas and the number of peaks of the concentration of the analyte present in each of the air samples; g) determining a confidence interval based on the number of peaks of the concentration of the tracer gas and the number of peaks of the concentration of the analyte; and H) controlling operation of the vehicle based on a function of the confidence interval and the concentration of the analyte present in the air sample.

Description

[0001] Citations to pending prior patent applications

[0002] This patent application:

[0003] (i) This is a continuation-in-part of pending prior U.S. patent application Ser. No. 17 / 462,318, filed on August 31, 2021, by the Automotive Coalition for Traffic Safety, Inc., for “SENSOR SYSTEM FOR PASSIVE IN-VEHICLE BREATH ALCOHOL ESTIMATION” (Agent Docket No. ACTS-108460-0009-101CON), which:

[0004] (a) This is a continuation of prior U.S. patent application Ser. No. 15 / 389,724 filed by the Automotive Coalition for Traffic Safety on December 23, 2016, for “SENSOR SYSTEM FOR PASSIVE IN-VEHICLE BREATH ALCOHOL ESTIMATION” (Agent Docket No. ACTS-108460-0009-101), which is filed as follows:

[0005] (1) Claims the benefit of prior U.S. Provisional Patent Application Serial No. 62 / 312,476 filed on March 24, 2016, by the Automotive Coalition for Traffic Safety, Inc., for “SENSOR SYSTEM FOR PASSIVE IN-VEHICLE BREATH ALCOHOL ESTIMATION” (Attorney Docket No. ACT-108460-0009-001); and

[0006] (ii) Claims the benefit of pending prior U.S. provisional patent application serial number 63 / 562889 filed on March 8, 2024, by the Automotive Coalition for Traffic Safety, Inc. for “SENSOR SYSTEM FOR PASSIVE IN-VEHICLE BREATH ALCOHOL ESTIMATION” (attorney docket number ACTS-1PROV).

[0007] The four (4) aforementioned patent applications are hereby incorporated herein by reference. Technical Field

[0008] The present invention relates to a method for detecting breath alcohol concentration in a driver's exhaled breath, and more particularly to a rapid estimation of a driver's breath alcohol level. Background Art

[0009] Working to prevent drunk driving, supervised breath tests are regularly performed by police officers.

[0010] In addition to supervised breathalyzer tests, automatic ignition interlock devices (sometimes called "alcohol locks") have been installed in vehicles themselves, which perform unsupervised testing to prevent vehicles from being operated by intoxicated drivers. The sensing technology used for such breathalyzer tests can be based on catalytic beads (or catalytic sensors (pellistors)), semiconductors, fuel cells, or infrared spectroscopy. Fuel cells are the primary sensing element used in breathalyzers and alcohol locks that include a mouthpiece. Evidence instruments typically use infrared spectroscopy. Catalytic beads, catalytic sensors, etc. are commonly used in low-cost devices for the consumer market and generally do not meet the requirements for analytical specificity. Typical breathalyzer devices provide a signal representing the breath alcohol concentration (BrAC) after the driver takes a deep breath and empties his or her airway into a mouthpiece (mouthpiece), which is usually a separate disposable item for hygiene reasons. To ensure a correct determination, the tester is required to deliver a forced exhalation close to full lung capacity. This requires considerable time and effort, especially for people with limited abilities. More specifically, it should be appreciated that, given a typical population, there is extremely wide variation in what is considered "full lung capacity." Certain passive breathing tests performed according to the present invention are possible without the need to obtain forced breaths close to full lung capacity for a given population (which would otherwise be necessary if active breathing tests were performed). It will be appreciated that the present invention typically utilizes breath sample volumes that are well below the full lung capacity of a typical adult (e.g., 0.7-1.2 L).

[0011] Ease of use, convenience, and accuracy are important factors in increasing the acceptance and adoption of built-in ignition interlock devices in vehicles. Summary of the Invention

[0012] Therefore, there is a need for a passive breath test that is flexible enough to avoid inconvenience to the driver while ensuring the accuracy of the test under various environmental conditions and driver behavior. In a passive breath test, the driver does not need to provide direct air to the sensor, and the BrAC measurement will be made from the air inside the vehicle without additional action by the driver, which will be a mixture of the driver's and any passenger's breath and ambient air. In contrast, in an active breath test, the driver may be required to approach the sensor and direct forced undiluted breath toward the sensor or through an air inlet (e.g., blowing into a tube). Although passive breath testing is preferred, under some conditions, it may not be possible to perform an accurate passive breath test. Such conditions may be environmental (e.g., very hot weather) or the result of the driver attempting to thwart the system (some examples are described below), but either way, the air inside the vehicle may not accurately reflect the driver's BrAC. If the normal test conditions under which an accurate passive BrAC test is possible are not met, an active breath test is required.

[0013] Various parameters indicative of ambient conditions and driver behavior are measured to detect when normal test conditions are no longer met. These include, for example, detecting a peak in tracer gas concentration, which indicates that the driver's breathing has been detected. A timer can set a time limit between the time the driver's presence is detected and the time the peak in tracer gas concentration is detected. This time limit can prevent the driver from attempting to thwart the system by holding his or her breath or otherwise hiding his or her breathing from the sensors. A pressure sensor can detect situations in which the driver attempts to thwart the system by ventilating the vehicle, or situations in which wind blowing through the vehicle may prevent accurate passive breath testing. Detecting the position of the driver's head relative to the sensor can ensure that the driver's breath is directed towards the sensor, so as to prevent attempts to thwart the system by supplying alternative sources of the "breath" to be measured.

[0014] The methods and apparatus described herein allow for passive detection of breath alcohol concentration and can be used to control the ignition of a vehicle. In particular, the methods and apparatus are designed to determine BrAC from a passive breath test during normal testing conditions without inconvenience to the driver, detect when normal testing conditions are no longer met, and provide a BrAC measurement from an active breath test under these circumstances.

[0015] In an example of a method or apparatus for passive breath alcohol testing of an operating vehicle, the apparatus may include a sensor that measures the concentration of a tracer gas in a passively obtained first air sample, and the method may include activating the sensor system, passively obtaining the first air sample, and measuring the concentration of the tracer gas from the first air sample. The apparatus may include a processor that uses the sensor system to determine a set of test conditions based in part on the first air sample, and the method may include this determination. If the set of test conditions is within a normal range and a peak in the tracer gas concentration is detected, the method or processor measures the driver's BrAC from the first air sample. If the set of test conditions is outside the normal range or no peak in the tracer gas concentration is detected, the method or processor requests an active second air sample from the driver and measures the driver's BrAC.

[0016] In some embodiments, the method includes measuring a time interval between activating the sensor system and detecting a peak in the tracer gas concentration. In some embodiments, the device includes a timer for measuring the time interval. If the time interval exceeds a predetermined time limit, the method or processor determines that the set of test conditions is outside a normal range. In some embodiments, the device includes a sensor for measuring an ambient condition of the vehicle, and in some embodiments, the method includes measuring such ambient condition. In some embodiments, such a sensor may be a temperature sensor, and in some embodiments, the method includes measuring the temperature within the vehicle. If the temperature is outside a normal temperature range, the method or processor determines that the set of test conditions is outside a normal range. In some embodiments, the device includes a pressure sensor for measuring pressure within the vehicle, and in some embodiments, the method includes measuring that pressure. If the pressure is outside a normal pressure range, the method or processor determines that the set of test conditions is outside a normal range. In some embodiments, the device includes a camera for measuring the position of the driver's head relative to the BrAC sensor, and in some embodiments, the method includes measuring the position of the driver's head relative to the BrAC sensor. In some embodiments, activating the sensor system includes detecting the presence of the driver entering the vehicle. In some embodiments, measuring the driver's BrAC from the active breathalyzer test includes determining whether the BrAC measured from the passive breathalyzer test is at a moderate level. If the measured BrAC is at a medium level, the method requests an active breath sample and measures BrAC. In some embodiments, measuring the driver's BrAC from the active breath test includes requesting an undiluted breath sample directed to a BrAC sensor via a human machine interface (HMI).

[0017] In some embodiments, the method includes sending a sensor signal to a central processing unit (CPU) of a breath test system that communicates with a CPU of the vehicle. In some embodiments, a processor receives the sensor signal from the sensor. In some embodiments, the method includes disabling operation of the vehicle if the result of the driver's BrAC measurement is above a set point, which may also be accomplished by the processor. In some embodiments, the method includes enabling operation of the vehicle if the result of the driver's BrAC is below a set point, which may also be accomplished by the processor. In some embodiments, the method includes requesting an active second air sample from the driver and measuring the driver's BrAC if the result of the passive breath test of the first air sample is at a medium level. In some embodiments, the request may be made by the processor. In some embodiments, the method includes continuously measuring the air sample after activating the sensor system and continuously measuring the concentration of the tracer gas after measuring the first air sample. In some embodiments, the sensor continuously measures the air sample after activating the sensor system and also continuously measures the concentration of the tracer gas after measuring the first air sample.

[0018] In some embodiments, the method and apparatus are designed to accumulate sensor signal information over a series of breaths until a desired confidence level is reached for the analyte measurement.

[0019] In a preferred form of the invention there is provided a method for passive breath alcohol testing, the method comprising:

[0020] A) passively obtaining a first air sample from air within a vehicle interior;

[0021] B) determining the concentration of: (i) a tracer gas and (ii) an analyte present in said first air sample;

[0022] C) passively obtaining a second air sample from the air within the vehicle interior;

[0023] D) determining the concentration of: (i) the tracer gas and (ii) the analyte present in the second air sample;

[0024] E) continuing to passively obtain a number N of air samples from the air within the vehicle interior and, for each air sample obtained, determining the concentration of the tracer gas and the analyte present in the air sample;

[0025] F) determining the number of peaks of the concentration of the tracer gas and the number of peaks of the concentration of the analyte present in each of the air samples;

[0026] G) determining a confidence interval based on the number of peaks in the concentration of the tracer gas and the number of peaks in the concentration of the analyte; and

[0027] H) controlling operation of the vehicle based on a function of the confidence interval and the concentration of the analyte present in the air sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further features of the present subject matter, its nature and various advantages will become apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which like reference characters refer to like parts throughout, and in which:

[0029] Figure 1 depicts a flow chart of a process for determining a BrAC measurement from a passive or active breath sample according to an illustrative implementation;

[0030] Figure 2 depicts a flow chart of a process for determining results of a BrAC measurement from a passive breath sample according to an illustrative implementation;

[0031] Figure 3 depicts a flow chart of a process for determining results of a BrAC measurement from an active breath sample according to an illustrative implementation;

[0032] Figure 4 depicts a sensor for detecting breath and BrAC concentrations from active and passive breath samples according to an illustrative implementation;

[0033] Figure 5A and Figure 5B is a top view of the position of a driver's head relative to a sensor according to an illustrative implementation;

[0034] Figure 6 is a graph representing an example of signals detected by a startup sensor and a BrAC sensor according to an illustrative implementation;

[0035] Figure 7 is a flow chart illustrating a method for accumulating sensor signal information over a series of breaths until a desired confidence level is reached for an analyte measurement;

[0036] Figure 8 is a flow chart illustrating another method for accumulating sensor signal information over a series of breaths until a desired confidence level is reached for an analyte measurement; and

[0037] Figure 9 is a graph representing an example of signals detected by a startup sensor and a BrAC sensor according to another illustrative implementation. DETAILED DESCRIPTION

[0038] background

[0039] Breathalyzing drivers is an effective screening method for reducing intoxicated driving and intoxicated driving-related deaths. During a breathalyzer test, a subject exhales air into a sensor or measuring device for a sufficient time and volume to achieve respiratory flow originating in the alveoli of the lungs, where substances in the blood, such as ethanol (EtOH), are exchanged with air. The sensor or measuring device then measures the airborne alcohol content (BrAC), which is correlated to blood alcohol using a conversion algorithm.

[0040] Existing breath-based alcohol testing technologies require the driver to deliver a forced breath close to full lung capacity. This often requires a significant amount of time and effort, especially for people with limited lung capacity. For hygiene reasons, the mouthpieces used in existing breath testing devices may also need to be cleaned and replaced after multiple uses. In addition, environmental conditions (e.g., wind, temperature, the presence of other people, etc.) may significantly affect the accuracy of BrAC measurements. In order to increase the adoption and public acceptance of ignition interlock devices in vehicles, a breath testing system that does not inconvenience the driver and is robust under the various conditions found in vehicles is needed.

[0041] Therefore, there is a need for a passive breath test that is flexible enough to avoid inconvenience to the driver while ensuring the accuracy of the test under various environmental conditions and driver behavior. In a passive breath test, the driver does not need to provide direct air to the sensor, and the BrAC measurement will be made from the air inside the vehicle, which will be a mixture of the breath of the driver and any passengers and the ambient air, without additional action by the driver. In a passive breath test, the air inside the vehicle is drawn into the sensor by a fan. The BrAC measurement is made by first measuring the concentration of a tracer gas (e.g., carbon dioxide), which indicates the dilution of the driver's breath in the air inside the vehicle. The measured EtOH concentration can then be combined with this breath dilution factor to determine the BrAC. Thus, the BrAC measurement is made without inconvenience to the driver and simply by sampling the air inside the vehicle.

[0042] In contrast, in an active breath test, the driver may be required to approach the sensor and direct forced, undiluted breath toward the sensor or through an air inlet (e.g., by blowing through a tube). In an active breath test, BrAC is thus measured directly from the driver's breath, rather than from the air inside the vehicle. An active breath test requires an action by the driver that is separate from the normal action required to start the vehicle and may therefore be considered less convenient than a passive breath test.

[0043] While passive breath testing is preferred, under certain conditions, it may not be possible to perform an accurate passive breath test. For example, the driver may attempt to obstruct the system, resulting in the air inside the vehicle not accurately reflecting the driver's BrAC. Similarly, environmental conditions inside the vehicle (e.g., strong winds from open windows, or high temperatures after the vehicle remains enclosed on hot days) may not allow for accurate BrAC measurement. If normal test conditions under which an accurate passive BrAC test can be performed are not met, the driver will be required to perform an active breath test.

[0044] The present invention provides various sensing checks to allow for passive detection and estimation of the driver's BrAC under normal conditions, while switching from active breath testing to BrAC measurement when normal conditions are no longer met. This reduces driver inconvenience by defaulting to passive BrAC estimation while providing an alternative logic path when the accuracy of the BrAC estimate is unclear or when driver behavior or test conditions exceed standards.

[0045] BrAC measurements from passive or active breath samples

[0046] Figure 1 A flow chart of a process for determining a BrAC measurement from a passive or active breath sample according to an illustrative implementation is depicted. Process 100 begins at 102. Start 102 can be initiated by unlocking the vehicle door with a wireless door key, by opening the door to the driver's seat, or any other indicator that can signal that the driver has entered the vehicle. When the driver or test subject takes the first step into the driver's seat of the vehicle, at 104, process 100 activates a sensor to monitor test conditions within the vehicle, detects the driver's breathing, and starts a timer to check whether the driver's breathing is detected within a time limit during the test. If the driver's breathing is detected (as determined at logic gate 106), the test conditions within the vehicle are normal (as determined at logic gate 108), and the time limit has not been exceeded (as determined at logic gate 110), process 100 proceeds to 112 and a BrAC measurement from a passive breath sample is taken. However, if either logic gate 106 or 108 makes a negative determination, or the time limit has been exceeded at 110 , process 100 will continue to request an active breath sample from the driver at 114 .

[0047] The test at 104 includes a self-test of all functional blocks and sensors used in process 100. At test 104, a stable operating temperature of the temperature sensitive element of any sensor used in process 100 is established.

[0048] This can include, for example, heating the mirror within the tracer gas detection sensor to above 40°C. Figure 4The mirror and tracer gas detection sensor are described in more detail. Under test conditions at or above room temperature, the self-test procedure performed at 104 can last between 5 and 8 seconds. At low temperatures, the self-test procedure may last longer than 8 seconds. The test at 104 may also require measuring initial vehicle conditions before the driver enters, such as CO2 levels, EtOH concentration in the vehicle air, air temperature, air pressure, etc. These initial conditions can be used to determine whether the driver's breathing is detected and whether the test conditions are within normal range at logic gates 106 and 108, respectively.

[0049] The tracer gas can be any gas used to detect the driver's breath. The tracer gas can be carbon dioxide (CO2) or any other gas that can be indicative of exhaled breath. The sensitivity of the tracer gas detection sensor allows detection of highly diluted exhaled gas, which may have a dilution factor (i.e., the ratio between ambient air and undiluted breath) greater than or equal to 50. After the startup process 100, air is continuously drawn from the air within the vehicle through the tracer gas detection sensor. The tracer gas detection sensor can be located closer to the driver's head than any passenger position, for example, on the steering column or side door closest to the driver's side of the vehicle. The exhaled breath is identified by the tracer gas detection sensor as a signal peak output. If the tracer gas is CO2, the baseline concentration of CO2 corresponding to the baseline signal is expected to be between 400 and 600 ppm (0.04%-0.06% by volume). The tracer gas signal and startup signal of 102 are referred to below. Figure 6 The tracer gas detection sensor that determines whether breathing is detected at logic gate 106 is described in further detail below. Figure 4 As described in further detail, the breath sample in which the tracer gas detection peak is found may be the same breath sample used for the BrAC measurement at 112. Thus, detecting the driver's breathing during test 104 and logic gate 106 may occur approximately simultaneously with the BrAC measurement from the passive breath sample taken at 112.

[0050] Logic gate 108 may process the test conditions of the vehicle and determine whether they are within normal conditions that can produce accurate BrAC measurements from passive breath samples.

[0051] Environmental conditions may require both the driver's behavior and the state of the vehicle itself. These conditions may be detected by various sensors, including tracer gas detection sensors, and auxiliary sensors placed throughout the vehicle. The sensors may include temperature sensors for determining the temperature within the vehicle, and pressure sensors for determining the atmospheric pressure within the vehicle and the wind or air moving through the interior of the vehicle. Normal temperatures within a vehicle may be in the range of -40°C to 85°C. This may be the temperature range within which a BrAC sensor is able to perform an accurate passive breath test. Normal atmospheric pressure may be in the range of 80 to 105 kPa. This may be the pressure range within which the driver's breath mixing with the surrounding air is able to produce an accurate passive breath test. The temperature and pressure sensors may be any standard sensor elements and may be embedded in the body of the vehicle.

[0052] A camera sensor for monitoring driver behavior can also be placed near the driver, such as near the steering column. The camera sensor can detect the position of the driver's head relative to the tracer gas detection sensor, as described in further detail below with reference to FIG5 . The relationship between the driver's head and the tracer gas detection sensor can determine whether the driver is breathing in the direction of the tracer gas detection sensor. The camera can detect situations in which the driver attempts to avoid detection of his or her BrAC by turning his or her back to the sensor. The camera sensor can also detect the presence of unfamiliar objects near the driver's face, such as masks, filters, spray bottles, or other objects intended to interfere with the tracer gas detection sensor or provide an alternative source of "breath" to prevent accurate passive breath testing. The camera sensor can also detect nearby passenger positions that may make it difficult to distinguish between the passenger's BrAC level and the driver's BrAC level, or in which the driver attempts to have the system measure the passenger's BrAC level instead of his or her own.

[0053] Logic gate 108 can also determine the state of the vehicle's heating, ventilation and air conditioning (HVAC) system, such as whether it is in an on state or an off state. During process 100, the HVAC system is preferably off or in normal operating conditions. Using the HVAC system during a passive breath test may over-dilute the driver's EtOH level, move the driver's breath away from the sensor, or otherwise hinder an accurate passive breath test. Logic gate 108 can also detect the presence of windshield fluid. Windshield fluid typically contains ethanol, which may affect the detection of EtOH in the vehicle. Under normal test conditions, the windshield fluid is in an off state. Logic gate 108 can determine the state of the vehicle's HVAC system and the state of the windshield fluid by communicating with the vehicle (e.g., communicating with the vehicle's CPU or controller area network (CAN) bus).

[0054] At 110, a logic gate determines whether the time limit of the process 100 for detecting the driver's breathing has been exceeded during the test 104. This can be a predetermined time limit, for example, from 10 to 30 seconds. If more than one tracer peak is detected within the time limit, the average and difference between each BrAC reading can be used to increase confidence in the classification into the "high," "intermediate," and "low" categories, as further described below. The accumulated tracer concentration is the primary factor in increasing confidence by increasing the accumulated signal-to-noise ratio. More specifically, if more than one peak in the tracer gas concentration is detected within the time limit, the average of the multiple BrAC concentration measurements (i.e., where each BrAC concentration measurement coincides with a detected peak in the tracer gas concentration) and the difference between each BrAC reading (i.e., the change in area under each peak of the consecutive BrAC concentration signals) can be used to increase confidence in the accuracy of the classification of the BrAC measurement. By way of example and not limitation, a set of accumulated BrAC concentration measurements taken over a predetermined time period can be used to calculate the driver's BrAC, where the confidence in the calculated BrAC is categorized as "high confidence," "medium confidence," and "low confidence," as discussed in further detail below. The accumulated tracer gas concentration (i.e., as determined by multiple tracer gas concentration measurements) is the primary factor in increasing confidence by increasing the accumulated signal-to-noise ratio. If it is determined at 110 that the time limit has been exceeded, process 100 proceeds to 114 for a BrAC measurement from an active breath sample. The time limit can prevent the driver from avoiding breathing in the direction of the sensor, holding their breath, wearing a mask over their head, or otherwise attempting to operate the vehicle without providing a breath sample. In this case, the logic gate at 110 will recognize that no breathing has been detected after the predetermined time limit and will request an active breath sample from the driver at 114.

[0055] If the driver's exhaled breath is detected at logic gate 106, logic gate 108 has determined that the test conditions are normal, and logic gate 110 has determined that the time limit has not been exceeded, process 100 will proceed to measure BrAC from a passive breath sample at 112. Figure 2 The BrAC measurement 112 is described in more detail. However, if no breathing is detected at 106, the process 100 will continue to test the driver's breathing until the time limit is exceeded at 110 or unless the normal test conditions are not met at 108. In this case, the process 100 will require an active breath sample to measure BrAC at 114. The determination at 108 that the normal test conditions are not met is sufficient to require an active breath sample at 114. Similarly, if it is determined at 110 that the time limit has been exceeded, the process 100 will proceed to the active breath sample at 114. Figure 3The active breathing sample at 114 is described in more detail.

[0056] The results of BrAC measurements 112 and 114 may differ in accuracy.

[0057] BrAC measurements from passive breath samples

[0058] Figure 2 A flow chart of a process for determining the results of a BrAC measurement from a passive breath sample according to an illustrative implementation is depicted. Process 112 determines the driver's BrAC at 202. Figure 1 As shown in FIG, process 112 may be performed approximately simultaneously with the detection of tracer gas at 104 and 106. Thus, process 112 may be performed using the same breath sample collected at 104 to detect a peak of tracer gas indicative of the driver's breathing. In other words, if breathing is detected at logic gate 106 within the time limit established at 104 upon initiation of process 100, process 112 may proceed to determine the driver's BrAC using the first breath sample identified at logic gate 106. The measurement of BrAC is based on the dilution of the detected tracer gas (which may be CO2). The detected dilution factor, or DF, of the tracer gas in the ambient air of the vehicle is used to determine an estimate of the driver's BrAC. The BrAC level may be determined according to the following equation:

[0059] BrAC = EtOH * DF (Equation 1)

[0060] DF is the dilution factor of the tracer gas in the air, i.e., DF is the ratio between the end-exposed (undiluted) tracer gas concentration and the tracer gas concentration measured by the sensor. Additional algorithms that incorporate information from auxiliary sensors (not shown) may be used. The algorithm used to measure BrAC from a passive breath sample at 112 is essentially the same as the algorithm used to measure BrAC from an active breath sample at 114. It will be appreciated that when measuring BrAC from a passive breath sample at 112, DF is much greater than when measuring BrAC from an active breath sample at 114. Figure 2As shown in FIG, if the estimated BrAC value is below a predetermined set point (denoted as "low" or "L"), process 112 outputs a signal at 206 indicating that the driver's BrAC is "normal." The predetermined set point may be in the range of 0.1 to 0.4 mg / L (50 to 200 ppm). The predetermined set point may be a function of the driver's age. The predetermined set point may be a function of the legal limit for blood alcohol concentration for driving under the influence (DUI) or driving while impaired (DWI). Signal 206 may be used to enable operation of the vehicle. If the estimated BrAC value is significantly above the predetermined set point (denoted as "high" or "H"), process 112 outputs a signal at 204 indicating that the driver's BrAC is "abnormal." By way of example and not limitation, a BrAC level of 0.1-0.2 mg / L (50 to 100 ppm) above the set point may result in outputting a signal at 204 indicating that the driver's BrAC is "abnormal." Signal 204 may be used to disable operation of the vehicle. If it is determined at 202 that the driver's BrAC is in the medium range (denoted as "Medium" or "I") slightly above or below a predetermined set point, further analysis of the driver's breathing is required to make a final determination. The driver is then asked to perform an active breath test at 208. Figure 3 The active breathing test is described in more detail and is Figure 1 and Figure 3 The process shown in 114. Sensors (e.g. Figure 4 The sensor described in ) can be measured at 202, while external processing (such as Figure 4 Signals 204 and 206 may be communicated to a central processing unit or CPU 415 (described in more detail in ).

[0061] BrAC measurements from active breath samples

[0062] Figure 3 A flow chart depicts a process for determining the results of a BrAC measurement from an active breath sample, according to an illustrative implementation. Process 114 begins at 302, where the driver's BrAC is measured. During the BrAC measurement from the active breath sample at 302, the driver is requested to provide an active breath to a sensor (not shown) at a distance of 15-30 cm from the sensor. This distance can be adjusted for the sensor's location within the vehicle. If the BrAC is below a predetermined set point (denoted as "low" or "L"), process 114 outputs a signal at 306 that the driver's BrAC is "normal."

[0063] Signal 306 may be used to enable operation of the vehicle. If the estimated BrAC value is significantly above a predetermined set point (denoted as "High" or "H"), process 114 will output a signal at 308 indicating that the driver's BrAC is "Abnormal." Signal 308 may be used to disable operation of the vehicle. If, at 302, it is determined that the driver's BrAC is within a medium range (denoted as "Medium" or "I"), slightly above or below a predetermined set point, the driver will be requested to provide a breath sample of evidential accuracy at 304. The breath test performed at 304 will require an undiluted breath sample. From test 304, there is no Medium response. The breath test at 304 will require the driver to actively breathe toward a sensor (not shown) at a distance of 15-30 cm from the sensor. This distance may be adjusted for the location of the sensor within the vehicle. If the measured BrAC value is below the set point (L), process 114 will generate an output signal at 306 indicating that the driver's BrAC is "Normal." If the measured BrAC value is above the set point (H), process 114 will generate an output signal at 308 indicating that the driver's BrAC is “not normal.”

[0064] Figure 1 Logic gates 106, 108, 110 in Figure 2 Logic gate 202 in, and Figure 3 The logic gates 302 and 304 in FIG. 4 are shown as representing "IF...THEN" logic statements, however, these logic gates are not limited to elements of Boolean logic. The logic gates 106, 108, 110, 202, 302, and 304 may also exhibit fuzzy logic or be governed by an artificial neural network. It is contemplated that the logic system may be programmed into the CPU 415, as described with reference to FIG. Figure 4 described in further detail.

[0065] Sensor for detecting breath and BrAC concentrations from both active and passive breath samples

[0066] Figure 4 A sensor for detecting breath and BrAC concentrations from both active and passive breath samples is depicted according to an illustrative implementation. Figure 1 As shown in FIG, the sensor 400 can detect breathing during the test 104, measure the initial condition of the vehicle at 104, and perform the following steps: Figure 1 BrAC measurements 112 from passive breath samples and 114 from active breath samples are shown in FIG. Figure 2 and Figure 3 The sensor 400 continuously draws air through the inlet 402, passes that air to the outlet 403, and measures both the presence of a tracer gas (eg, CO2) and the presence of EtOH within the air stream. Figure 2 and Figure 3 As described, sensor 400 determines whether the driver's BrAC is in the low, high, or medium range.

[0067] Sensor 400 is contained within housing 401 and can be a stand-alone sensor or designed for integration into the vehicle interior, such as within the steering column, side door, A- or B-vertical pillar, sun visor, dashboard, or other convenient location in the vehicle that is significantly closer to the driver's head than to the designated passenger area. Housing 401 can be airtight except for openings at sensor inlet 402 and outlet 403. Housing 401 can have dimensions of approximately 25×40×120 mm. Air brought into housing 401 through inlet 402 is heated to above body temperature by inlet heater 404, which can prevent condensation in low ambient temperatures. Inlet heater 404 can have a large surface contact area with the inlet air to improve heat transfer from the heater to the incoming air. Heater 404 can be a resistive heater. Airflow from inlet 402 to outlet 403 is driven by fan 411 located near outlet 403.

[0068] Sensor 400 measures the presence of both CO2 and EtOH through infrared (IR) spectroscopy. IR spectroscopy uses the unique "fingerprint" produced by vapor-phase alcohol when illuminated by infrared light to determine the alcohol concentration within the airstream of sensor 400. The detected absorption spectrum of any substance is the product of resonant molecular vibrations specific to the atomic bonds within the molecules or compounds in the breath sample. Based on the absorption spectrum, the specific substance within the breath sample and its absolute or relative concentration can be determined.

[0069] To perform IR spectroscopy and detect both the presence of tracer gas and the presence of EtOH, the sensor air chamber tube 410 includes two independent optical paths, one for the detection of tracer gas and a second for the detection of EtOH. The signals generated by these two optical paths are used to determine the dilution factor value (or DF as shown in Equation 1) of the driver's breath in the ambient air and the EtOH concentration value within the input air.

[0070] like Figure 4As shown in , a first optical path consisting of an EtOH IR emitter 406 and an EtOH IR detector 407 will determine the EtOH concentration. The EtOH IR emitter 406 outputs IR radiation into the interior of the sensor air chamber tube 410. A spherical mirror assembly consisting of a first mirror 405 placed at one end of the air chamber tube 410 and a second mirror 412 located at the opposite end of the air chamber tube 410 reflects the IR radiation emitted from the EtOH IR emitter 406. The optical path length of the emitted IR radiation can be several times the length of the distance between the first mirror 405 and the second mirror 412 because the mirror assembly will reflect the emitted light several times before it hits the EtOH IR detector 407. The mirrors 405, 412 preferably include a layer of highly reflective material (such as gold or aluminum) and a very thin protective surface layer on their reflective surfaces to maintain high reflectivity even if the air chamber tube 410 is subjected to corrosive gases during its operating life. The optical path in Figure 4 407, the infrared radiation beam may pass through the optical unit from the emitter 406 a number of times, for example sixteen times (or any multiple of four), before it hits the detector 407.

[0071] The EtOH IR emitter 406 can be a black body radiator, an IR laser diode, or any other light source capable of generating IR light, and preferably has a low mass to fit within the air chamber tube 410. The EtOH IR emitter 406 can be modulated at a frequency between 5-10 Hz in order to suppress low frequency noise and interference in the signal of the EtOH IR detector 407. The EtOH IR detector 407 includes a band pass filter tuned to the IR absorption peak of EtOH, which is approximately 9.5 μm. The EtOH IR detector 407 can be a thermoelectric or photon detector capable of generating a high resolution signal, and can also include a Peltier element for local cooling in order to suppress thermal noise in the detection signal. Reference Figure 6 The detection signal produced by EtOH IR detector 407 is described in more detail. Sensor 400 is specifically designed for high resolution IR spectroscopy and can have a resolution of over 0.5 μg / L (or 1.2 ppm) for EtOH, enabling estimation of alcohol concentration in highly diluted breath.

[0072] The second optical path is dedicated to detecting the presence of a tracer gas (e.g. CO2) which would indicate a dilution of the driver's breath in the air input via the sensor 400. The tracer gas IR emitter 408 is positioned opposite the tracer gas IR detector 409 so that the optical path from the tracer gas IR emitter 408 to the tracer gas IR detector 409 spans the shorter dimension of the air chamber tube 410. The tracer gas IR detector 409 may be tuned to a wavelength band specific to the IR absorption frequency of the detected tracer gas. In the example where the tracer gas is CO2, the absorption peak may be at 4.26 μm. Due to the high end tidal concentration of CO2 in exhaled air (typically 4.2% by volume), a short optical path across the air chamber tube 410 may be used. This path is Figure 4 Indicated as a dashed line between the tracer gas IR emitter 408 and the tracer gas IR detector 409. Figure 6 The signal produced by the tracer gas IR detector is described in more detail.

[0073] The signals from both the EtOH IR detector 407 and the tracer gas IR detector 409 can be used to determine whether normal conditions for passive measurement of BrAC are met, such as in Figure 1 104 and logic gate 108 of process 100 shown in FIG. The process may need to check that the baseline presence of the tracer gas is within a standard level, such as a baseline concentration of CO2 in the ambient air.

[0074] like Figure 4 As shown in FIG, first mirror 405 and second mirror 412 are both in communication with a central processing unit or CPU 415. EtOH IR emitter 406, EtOH IR detector 407, tracer gas IR emitter 408, and tracer gas IR detector 409 are also in signal communication with CPU 415. CPU 415 processes the signals generated by EtOH IR detector 407 and tracer gas IR detector 409 to determine a BrAC measurement.

[0075] A human machine interface (HMI) 413 is in communication with the CPU 415 and can be used to communicate with the driver to request a BrAC measurement from an active breath sample. The HMI 413 includes audio-visual components (e.g., a screen and speakers) for communicating with the driver, which are used to convey messages and requests for active breath testing and other instructions to the driver. The HMI 413 can display the results of the BrAC measurement to the driver. The HMI 413 can be a multi-purpose interface, such that requesting and displaying information related to the breath test is just one of many functions. Other functions can be navigation, HVAC interaction, stereo system interaction, or other system interactions typical for a vehicle. The HMI 413 can be integrated into the vehicle, within the driver's field of view.

[0076] CPU 415 also communicates with auxiliary sensors 414, which may be, for example, temperature, atmospheric pressure, or optical sensors, or cameras, for determining test conditions within the vehicle. Auxiliary sensors 414 are used during test 104 of process 100. Data communication unit 416 can store parameter values ​​used by the CPU to determine BrAC measurements and normal test conditions for the vehicle. Data communication unit 416 also transmits data between sensor system 400 and other units (not shown) external to sensor 400. Sensor 400 also includes power unit 117 for power management and supply.

[0077] Measuring head position

[0078] Figure 5A is a top view of the position of the driver's head relative to the sensor according to an illustrative implementation. The auxiliary sensor measures a lateral distance 510 between the driver 502 and the sensor 506. The lateral distance 510 can be measured between the centerline 508 of the sensor 506 and the centerline 504 of the driver's head 502. Under normal test conditions, the lateral distance 510 is less than or equal to 20 cm. The measurement of the lateral distance 510 can occur at Figure 1 The test 104 of the process 100 shown in FIG. At logic gate 108, it is determined whether the test condition of the vehicle is normal taking into account the lateral distance 510, such as Figure 5A . The measurement of lateral distance 510 can ensure that the driver breathes directly toward sensor 506 during the active breath test. The measurement of lateral distance 510 can also ensure that during the passive breath test, the driver does not attempt to avoid the sensor's breathing detection by holding his or her head away from the sensor.

[0079] Next see Figure 5BThe auxiliary sensor also measures the rotation of the driver's head relative to the centerline 518 of the sensor 516. The rotation angle 520 can be measured between the centerline 518 of the sensor 516 and the centerline 514 of the driver's head 512. Under normal test conditions, the rotation angle 520 can be ±5°. The measurement of the rotation angle 520 can occur at Figure 1 1. Test 104 of process 100 shown in FIG.

[0080] At logic gate 108, it is determined whether the test condition of the vehicle is normal taking into account the following: Figure 5B . The measurement of rotation angle 520 can ensure that the driver breathes directly toward sensor 516 during the active breathing test. The measurement of rotation angle 520 can also ensure that during the passive breathing test, the driver does not try to avoid the sensor's breathing detection by holding his or her head away from the sensor.

[0081] The lateral distance 510 and the rotation angle 520 can be measured by an embedded camera sensor (not shown) that can be incorporated into the vehicle and placed near the driver's head. The embedded camera can also determine whether there are unfamiliar objects within the camera's field of view and / or whether a passenger is within the driver's field of view.

[0082] Signals detected by the start sensor and BrAC sensor

[0083] Figure 6 Is to use Figure 4 Graphs of examples of signals detected by sensor 400 for an illustrative implementation of the present invention are shown in FIG. The graphs shown at 600 occur along the same time scale. Graph 602 (denoted as "P") shows signal 604, which indicates that the presence of a driver is detected (e.g., as detected by auxiliary sensor 414) as he or she enters or prepares to enter the vehicle. Signal 604 initiates the Figure 1102 is shown in the process 100 of FIG. Signal 604 starts a timer that will determine the time interval between the start signal at 604 and the detection of a breath, which is shown at graph 606 (denoted as "T"). Breathing is detected from a peak 608 in the concentration of the tracer gas signal. When the tracer gas is CO2, assuming a dilution factor of 80 and an end-tidal CO2 concentration of 4.2% by volume, the peak in breath detection is characterized by an amplitude of CO2 detection equal to or greater than 525 ppm. The duration 614 of peak 608 is expected to be 1-3 seconds, excluding the response time of the sensor. The rise time and fall time 616 of peak 612 can also be used to characterize the tracer gas signal as a result of the driver's exhaled breath. Typical rise times can be in the range of 0.5 to 1.0 seconds, while typical fall times can be in the range of 3 to 5 seconds. The peak of the tracer gas signal at 610 can end the timer. The time interval 622 can be measured and used to determine the time between the start signal 604 and the point 610 in the respiration signal 608 (e.g., Figure 1 ) exceeds an acceptable time limit.

[0084] Graph 618 (denoted as "A") shows a detection signal for EtOH. Depending on the concentration of EtOH in the driver's breath, graph 618 may or may not show a peak 620 corresponding to peak 608 in the tracer gas. However, if there is EtOH in the driver's breath, then EtOH signal 620 will be approximately simultaneous with tracer gas signal 608, as shown in FIG. Figure 6 The amplitude of the peak in the EtOH signal 620 will indicate the concentration of BrAC in the measured breath sample. The measurement of BrAC from peak 620 can occur at approximately the same time as the detection of peak 608 in the tracer gas signal.

[0085] Passive BrAC estimation using accumulated sensor signal acquisition

[0086] In the previous section, BrAC estimation was performed by combining sensor signals representing tracer gases such as carbon dioxide (CO2) and ethanol vapor (EtOH). However, the present invention is not limited to these substances or to a specific position of the test subject (e.g., the driver in the driver's seat). It can be used in any situation where it is crucial to accurately estimate the breath concentration of any particular substance without disturbing the subject.

[0087] As mentioned above, a passive estimate of breath alcohol concentration (BrAC) can be performed by measuring the tracer gas concentration at the same location and performing the following calculation

[0088] BrAC = EtOH * DF (Equation 1)

[0089] where DF represents the dilution factor determined by dividing the end-tidal concentration of the tracer gas by the measured value at the sensor location. In the case of CO2 as the tracer gas, the end-tidal concentration is 4.2% by volume, and the corresponding value for water vapor is 5.5% by volume. In passive vehicular applications, DF can vary considerably.

[0090] The previous sections disclosed methods and apparatus for passively detecting an analyte (e.g., EtOH) by managing conditions related to signal stability, environmental influences, and subject behavior, all of which are necessary for accurate analyte estimation. When these conditions deviate from normal, the accuracy of the passive detection process may decrease, requiring the subject to provide an active breath sample.

[0091] In the following sections, modified methods and apparatus for passively detecting an analyte (e.g., EtOH) are disclosed. Such modified methods and apparatus can produce more accurate estimates of the analyte (e.g., EtOH). Such modified methods and apparatus are fundamentally based on the premise that the confidence level of the analyte estimate increases with increasing volume of the analyzed gas, i.e., accumulating sensor signal information over a series of breaths can increase the confidence level of the analyte measurement.

[0092] Some key features of this modified method and apparatus include:

[0093] - means for determining and repeatedly recording the instantaneous tracer gas concentration at a location near the driver's seat of a vehicle;

[0094] - means for determining and repeatedly recording the instantaneous alcohol vapor concentration simultaneously with and at the same location as the recording of the tracer gas concentration;

[0095] - means for quantifying the amplitude and timing of peaks in tracer gas concentration;

[0096] - means for calculating the cumulative breath alcohol concentration based on the peak amplitude and peak timing of the tracer gas (i.e., by using the instantaneous tracer gas and alcohol vapor concentrations);

[0097] - components for calculating cumulative confidence levels in breath alcohol concentration over time; and

[0098] - means for activating alarms and / or switches that enable and / or disable driving of the vehicle based on a combined result of the calculation of the average breath alcohol determination and a confidence level associated with a preset limit concentration.

[0099] Essentially, this form of the invention recognises that the confidence level of an analyte determination increases with increasing volume of gas analysed, ie the confidence level of an analyte determination increases with increasing number of breaths analysed.

[0100] Now see Figure 7 , there is shown a signal flow diagram corresponding to one embodiment of a modified method and apparatus for estimating BrAC. The system begins at 701 by unlocking the vehicle cabin door, and the startup phase 702 includes a self-test procedure that is used to check the operation of all system components. These procedures are normally fast, and the system is able to quickly and continuously record sensor signals corresponding to (i) local tracer gas concentration 703 and (ii) EtOH concentration 704. When the driver enters the vehicle cabin and delivers an exhaled breath, a tracer gas peak will appear at the sensor location, and the amplitude and timing of this peak will be determined by the incremental detector 705. This timing is used to trigger the determination of the amplitude of the corresponding EtOH peak by the incremental detector 706. Figure 9 A more detailed description of the functionality of the delta detectors 705, 706 is provided.

[0101] The tracer gas and EtOH signals 703, 704 are recorded continuously. As time passes, more signal peaks corresponding to the driver's exhaled breath are recorded and accumulated by adding the contributions from each detected peak with the aid of adder blocks 707 for the tracer gas signal and 708 for the EtOH signal.

[0102] The adder block signals 707, 708 are combined to enable the accumulated BrAC calculation 709 using the following equation:

[0103]

[0104] This equation can also be restated as:

[0105]

[0106] The CO2-related dilution factor (DF) is a quality indicator for both Equation 2 and Equation 3. Thus, it will be appreciated that for both Equation 2 and Equation 3, the smaller the value of the CO2-related dilution factor (DF) (i.e., corresponding to a higher measured CO2 value), the greater the weighting of the corresponding peak in Equations 2 and 3.

[0107] Then, in block 710, the confidence of the BrAC value is tested relative to: (i) criteria based on the legal limit or any other preset limit (e.g., a BrAC value of 0.08% or less may be required for operating a vehicle in the United States, a different BrAC value may be required for operating a vehicle outside the United States, etc.), and (ii) a desired confidence level in the calculated accumulated BrAC, which may vary from one application to another, e.g., a "high confidence level" may be required when the BrAC value is very close to (e.g., slightly above or slightly below) the legal limit for a given jurisdiction, a "medium confidence level" may be required when the BrAC value is greater than zero but still significantly below the legal limit for a given jurisdiction, and a "low confidence level" may be required when the BrAC value is significantly below (or significantly above) the legal limit for a given jurisdiction. If the desired confidence level for the particular application (e.g., "high confidence level," "medium confidence level," or "low confidence level") is achieved, a final lock / unlock function 711 is reached to determine the drivability of the vehicle. If the desired confidence level is not reached, additional accumulation of BrAC determinations will be required 709 (i.e., the system will continue to collect BrAC information from additional breaths of the driver until the desired confidence level is reached). Note that various factors may affect the confidence level associated with the determination of the analyte concentration, and these factors include, but are not limited to, sensor sensitivity, the number of breaths sampled, signal stability, environmental effects, and subject behavior. Note also that the confidence level attributed to the accumulated BrAC value is a function of the number of breaths analyzed to derive the accumulated BrAC value, which in turn is represented by the number of peaks in the measured tracer gas concentration.

[0108] In another form of the invention, and now see Figure 8 , the implementation of confidence block 809 is somewhat different and is based solely on the tracer gas signal. In this implementation of the present invention, and as will be discussed in more detail below, BrAC determination 810 is performed only when the accumulation of tracer peaks has reached a certain preset limit based on test results performed on the system. Lock / unlock function 811 is identical to lock / unlock function 711.

[0109] Therefore, in this form of the invention, and still with reference to Figure 8, the system starts at 801 by unlocking the cabin door, and the startup phase 802 includes a self-test procedure that is used to check the operation of all system components. These procedures are normally fast, and the system is able to quickly and continuously record sensor signals corresponding to the local tracer gas concentration 803 and EtOH concentration 804. When the driver enters the vehicle cabin and delivers an exhaled breath, a tracer gas peak will appear at the sensor location, and the amplitude and timing of this peak will be determined by the incremental detector 805. This timing is used to trigger the determination of the amplitude of the corresponding EtOH peak by the incremental detector 806. Similarly, the following description of the Figure 9 A more detailed description of the functionality of the delta detectors 805, 806 is provided.

[0110] The tracer gas and EtOH signals 803, 804 are recorded continuously. As time passes, more signal peaks corresponding to the driver's exhaled breath are recorded and accumulated by adding the contributions from each detected peak with the aid of adder blocks 807 for the tracer gas signal and 808 for the EtOH signal.

[0111] Then, in block 809, the confidence of the tracer gas value is tested relative to: (i) criteria based on a legal limit or any other preset limit (e.g., a BrAC value of 0.08% or less may be required to operate a vehicle in the United States, or a different BrAC value established by laws in a different jurisdiction, or another BrAC value set by the vehicle manufacturer, etc.), and (ii) a desired confidence level (e.g., "high confidence level," "medium confidence level," or "low confidence level"). If the desired confidence level is achieved, adder block signals 807 and 808 are combined to enable an accumulated BrAC calculation 810 using the equation BrAC=EtOH*DF. Note that Equations 2 and 3 may be used when it is desired to assign a higher statistical weight to the accumulated BrAC value for readings with higher peaks in the tracer gas (CO2) concentration than for readings with lower peaks in the tracer gas (CO2) concentration. It will be appreciated that when calculating the cumulative BrAC value, readings with high tracer gas concentrations should be given a higher statistical weight than readings with low tracer gas concentrations (i.e., because the EtOH concentration signal corresponding to a higher tracer gas concentration signal may be more likely to indicate breath in the chamber than an EtOH concentration signal corresponding to a lower tracer gas concentration signal, which may indicate the presence of partially / over-diluted breath in the chamber). If the desired confidence level is achieved, a final lock / unlock function 811 is reached, thereby determining the drivability of the vehicle. If the desired confidence level is not achieved, additional accumulation 810 of BrAC determinations will be required (i.e., the system will continue to collect tracer gas information from additional exhalations of the driver until the desired confidence level is achieved). Note that various factors may affect the confidence level associated with the determination of the analyte concentration, and these factors include, but are not limited to, sensor sensitivity, the number of breaths sampled, signal stability, environmental effects, and subject behavior, among others. Note also that the confidence level attributed to the cumulative BrAC value is a function of the number of breaths analyzed to derive the cumulative BrAC value, which in turn is represented by the number of peaks in the measured tracer gas concentration.

[0112] Figure 9 The schematic diagram shows typical tracer gas and EtOH concentration signals as a function of time. These tracer gas and EtOH concentration signals correspond to the concentrations of Figure 7 and Figure 8 The outputs of blocks 703, 803 and 704, 804 in FIG. Figure 9As can be seen in Figure 1, two peaks are observed in both the tracer gas and EtOH signals approximately 3 and 8 seconds after the starting point. The peaks correspond to the exhaled breath of the subject. Note that the two peaks 902, 905 in the tracer gas signal are detected by an incremental detector 705, which is essentially a slope detector for finding the peaks of the tracer gas signal. The tracer gas and EtOH signal samples (preferably recorded at a rate of more than five samples per second) are subjected to addition and subtraction operations in real time to detect upward or downward movements, thereby enabling the detection and quantification of the occurrence of peaks above a more or less noisy background. The tracer signal characteristics are peaks 902 and 905 surrounded by background values ​​901, 903 and 904, 906, respectively, which are obtained immediately before and after each peak. From these values, it is possible to calculate the amplitude of the peak. The use of multiple background points allows continuous monitoring of background changes, which is very useful for analyzing the background changes based on the Figure 7 and 8 (See below) The choice of scheme may be important. The variation of the background signal may be referred to as "noise". Such "noise" may originate from the fundamental, and / or depend on environmental factors such as temperature, humidity, transients, etc. Preferably, the "noise" is measured in real time by continuous and automatic sampling of both the tracer gas and EtOH signals during the peak detection and quantification period. The noise level can be quantified and correlated with the calculated BrAC peak level by comparing, for example, the root mean square (RMS) variation of the signal.

[0113] The BrAC reading will be derived from the tracer gas and EtOH signal peaks using equation (1). If the reading is well above (or below) the legal concentration limit, the BrAC reading can be used directly to classify between "high concentration" or "low concentration", supported by comparison with the actual noise level. In the case of "medium concentration", the actual noise level will also provide sufficient decision support. The BrAC reading taken in conjunction with the legal limits and noise levels for the particular jurisdiction in question will therefore determine the confidence level for classifying the breath alcohol concentration as "high confidence level", "medium confidence level" or "low confidence level". By adding more BrAC readings, the confidence level of the BrAC measurement increases (e.g., from "low confidence level" to "medium confidence level" or "high confidence level").

[0114] Combined with data on systematic measurement errors, the noise level can be used to define a confidence level for the BrAC readings using equation (1).

[0115] The timing of events 901-906 in the tracer gas signal can be linked to corresponding time points in the EtOH signal 1001-006 and enable calculation of the corresponding EtOH peak amplitudes (i.e., EtOH peaks 1002, 1005 correspond in time to tracer gas peaks 902, 905, respectively, and EtOH background values ​​1001, 1003, 1004, and 1006 correspond in time to tracer gas background values ​​901, 903, 904, and 906, respectively; also note that both peaks 1002, 1005 in the EtOH signal are detected by a delta detector 806, which is essentially a slope detector for finding peaks in the EtOH signal. According to Figure 9 The amplitude of the tracer gas peak in (ie, a peak of approximately 0.1), according to the above equation 1, taking into account the estimate of BrAC=0.25 mg / L, DF can be estimated to be approximately 80.

[0116] If the BrAC values ​​based on the first and second peaks are inherently different such that classification between "high," "medium," and "low" concentrations relative to the legal limit cannot be made within a particular confidence level (e.g., a "high confidence level," "medium confidence level," or "low confidence level"), then an active breath test may need to be obtained from the driver, or an overruling principle (e.g., a principle of minimizing the risk of personal injury) may be used to determine the drivability of the vehicle (e.g., suspending the drivability of the vehicle until the BrAC is determined to be below the legal limit for that particular jurisdiction with a "high" confidence level).

[0117] The above procedure will automatically compensate for slowly changing background values ​​in both the tracer gas and EtOH channels.Using continuous or digital signal acquisition followed by signal accumulation provides an enhancement of the signal-to-noise ratio.

[0118] When there is a stable background tracer gas concentration (which can be identified by relatively stable background values ​​901, 903 and 904, 906), Figure 8 The system outlined in may be advantageous. In this case, there will be a very strong correlation between the two signals (i.e., between the tracer gas signal and the EtOH signal). In the presence of passengers or other external sources of background variation, Figure 7 The solution shown in may be more advantageous.

[0119] Essentially, the present invention comprises a novel method and apparatus for determining, using multiple passive breath tests, whether a driver's calculated BrAC concentration (i.e., the accumulated BrAC concentration) is generally classified as "high" or "low." Furthermore, the present invention contemplates determining whether the accumulated BrAC concentration is assigned an appropriate confidence level (e.g., "high confidence level," "medium confidence level," "low confidence level") for a particular category of BrAC concentration, with the confidence level being a function, in part, of the total number of breaths analyzed to arrive at the accumulated BrAC concentration.

[0120] Modifications of the Preferred Embodiment

[0121] It will be understood that the foregoing is only illustrative of the principles of the invention and that the invention can be practiced by embodiments other than those described, which are presented for purposes of illustration and not limitation, and that the invention is limited only by the claims that follow.

Claims

1. A method for passive breath alcohol detection, comprising: A) passively obtaining a first air sample from air within a vehicle interior; B) determining the concentration of: (i) a tracer gas and (ii) an analyte present in said first air sample; C) passively obtaining a second air sample from the air within the vehicle interior; D) determining the concentration of: (i) the tracer gas and (ii) the analyte present in the second air sample; E) continuing to passively obtain a number N of air samples from the air within the vehicle interior and, for each air sample obtained, determining the concentration of the tracer gas and the analyte present in the air sample; F) determining the number of peaks of the concentration of the tracer gas and the number of peaks of the concentration of the analyte present in each of the air samples; G) determining a confidence interval based on the number of peaks in the concentration of the tracer gas and the number of peaks in the concentration of the analyte; as well as H) controlling operation of the vehicle based on a function of the confidence interval and the concentration of the analyte present in the air sample by providing a signal to the vehicle.

2. The method according to claim 1, wherein Passively obtaining air samples from the interior of the vehicle is initiated by unlocking a door of the vehicle using a wireless door key.

3. The method according to claim 1, wherein Passively obtaining an air sample from the interior of the vehicle is initiated by a person sitting in the driver's seat of the vehicle.

4. The method according to claim 1, wherein Before performing step (A), the method includes activating a sensor to monitor a test condition within the vehicle when a driver enters the vehicle, and obtaining a test sample from the interior of the vehicle.

5. The method according to claim 4, wherein The activating the sensor to monitor the test condition in the vehicle comprises at least one item from the group consisting of: (i) determining whether the tracer gas has been detected in the test sample; (ii) determining whether the test conditions are within predetermined parameters; as well as (iii) determining whether a predetermined time has elapsed after the sensor is activated to monitor the test condition.

6. The method according to claim 5, wherein: When all of the following conditions are met: (i) detecting a tracer in the test sample; (ii) the test conditions are within predetermined parameters; as well as (iii) the predetermined time has not elapsed after the sensor is activated to monitor the test condition; Proceed to step (A).

7. The method according to claim 5, wherein: When any of the following conditions are not met: (i) detecting a tracer in the test sample; (ii) the test conditions are within predetermined parameters; as well as (iii) the predetermined time has not elapsed after the sensor is activated to monitor the test condition; Perform an active breathing test.

8. The method according to claim 5, wherein The test conditions include at least one item selected from the group consisting of: a CO2 level in the air within the vehicle interior, an EtOH concentration in the air within the vehicle interior, a temperature of the air within the vehicle interior, an air pressure of the air within the vehicle interior, and a position of the driver's head relative to a tracer gas detection sensor.

9. The method according to claim 8, wherein The test condition is satisfied when the temperature of the air within the vehicle interior is between -40°C and 85°C, and is not satisfied when the temperature of the air within the vehicle interior is lower than -40°C or higher than 85°C.

10. The method according to claim 8, wherein The test condition is satisfied when the air pressure of the air within the vehicle interior is between 80 kPa and 105 kPa, and is not satisfied when the air pressure of the air within the vehicle interior is less than 80 kPa or greater than 105 kPa.

11. The method according to claim 8, wherein determining the position of the driver's head relative to the tracer gas detection sensor using a camera; wherein the test condition is satisfied when the driver's head is oriented so that the direction of breathing is in the direction of the tracer gas detection sensor; and Wherein, when the driver's head is oriented so that the direction of breathing is not in the direction of the tracer gas detection sensor, the test condition is not satisfied.

12. The method according to claim 1, wherein The tracer gas was CO2, and the analyte was ethanol (EtOH).

13. The method according to claim 12, wherein: The concentration of the tracer gas is plotted as a function of time to determine a maximum tracer gas concentration during a time period, and further wherein the maximum tracer gas concentration within the time period corresponds to the peak of the tracer gas concentration.

14. The method according to claim 13, wherein Breath is determined to be present in the air within the vehicle interior when the peak of the tracer gas corresponds to a concentration between 400 ppm and 600 ppm.

15. The method according to claim 5, wherein: The test condition includes an on / off state of an HVAC system within the vehicle, and further wherein the test condition is determined to be outside of predetermined parameters when the HVAC system is set to an on state.

16. The method according to claim 5, wherein The test condition includes the presence of windshield fluid, and further wherein the test condition is determined to be outside of predetermined parameters when windshield fluid is detected.

17. The method according to claim 1, wherein The confidence interval is classified as "high confidence", "medium confidence" or "low confidence", and further, wherein the classification of the confidence interval is a function of the number of peaks of the concentration of the tracer gas within a predetermined time period, wherein a greater number of peaks of the concentration of the tracer gas during the predetermined time period results in a classification of "high confidence" and a lower number of peaks of the concentration of the tracer gas results in a classification of "medium confidence" or "low confidence".

18. The method according to claim 5, wherein: If, after activating the sensor to monitor the test condition, the predetermined time has elapsed without detecting a peak of the tracer gas and the test condition is not determined to be within predetermined parameters, the driver is requested to provide an active breath sample.

19. The method according to claim 1, wherein If the concentration of the analyte does not exceed a predetermined set point, the signal provided to the vehicle indicates "low," and further wherein the "low" signal allows the vehicle to be operated.

20. The method according to claim 1, wherein If the concentration of the analyte exceeds a predetermined set point, the signal provided to the vehicle indicates "high," and further wherein the "high" signal disables operation of the vehicle.

21. The method according to claim 1, wherein If the concentration of the analyte exceeds a predetermined lower boundary point and does not exceed a predetermined upper boundary point, the signal provided to the vehicle is indicated as "medium".

22. The method according to claim 1, wherein The peak in the concentration of the tracer gas is determined by plotting the concentration of the tracer gas versus time, and further wherein the peak in the tracer gas is characterized by a peak having a concentration above 525 ppm and a duration between 1-3 seconds.

23. The method according to claim 22, wherein Each peak of the concentration of the tracer gas is characterized by a rise time and a fall time, wherein the rise time includes the time for the concentration of the tracer gas to rise from zero to the peak value, and wherein the fall time includes the time for the concentration of the tracer gas to fall from the peak value to zero.

24. The method according to claim 23, wherein The rise time is 0.5-1.0 seconds, and the fall time is 3.0-5.0 seconds.

25. The method according to claim 1, wherein For N number of air samples, providing N number of signals representing the concentration of the tracer gas and the concentration of the analyte present in each of the N number of air samples, and also including using an adder block to calculate the accumulated concentration of the analyte.

Images