Patent Grant
11472235
Driving on worn, low-tread, and low-pressure tires can create a safety hazard for the driver and passengers of a vehicle, as well as others who may encounter a vehicle traveling on worn, low-tread tires. For example, a vehicle traveling on worn, low-tread, and/or low-pressure tires may be unable to stop suddenly and efficiently while traveling on roads during inclement weather, such as rain, snow, ice, or mud. This can result in a collision involving the vehicle that could have been otherwise avoided, and such collisions can cause property damage and/or personal injury.
Tire treads are designed to maintain solid contact and grip on the road even during inclement weather. Driving on tires with insufficient treads (i.e., balding or low-tread tires) can provide an increased risk of hydroplaning and/or can result in decreased handling of the vehicle. Moreover, driving can create friction between tires and the road, and tire treads can function to help cool the tires, reducing the effects of the heat caused by driving. Low-tread tires can reduce the ability of the tire to cool, resulting in the heat experienced by the tires to reach unsafe levels. This can ultimately result in a blowout, which could cause a driver to lose control of a vehicle, especially while traveling at high speeds.
In addition, low-tread tires generally retain air less efficiently than tires with sufficient tread depth. Thus, low-tread tires can be more susceptible to becoming low-pressure tires. Improperly inflated tires are typically unable to properly grip the road, regardless of road conditions, making it more difficult for a driver to steer the vehicle. Improperly inflated tires can also cause a vehicle to skid during sudden stops, can reduce gas mileage of a vehicle, and/or can cause the tire tread to wear more quickly. As another example, low-tread tires can be more susceptible blowouts after suffering a puncture as the tire no longer have sufficient material to resist a blowout (e.g., resist shearing of the tire caused by the internal pressure of the tire) when the tire experiences a puncture.
Existing tires and related systems can include pressure sensors that can provide information regarding the pressure of the tire, but there is a need to track the tread depth of a tire, as well as other information that can be pertinent to the health of a tire.
These and other problems can be addressed by the technology disclosed herein, which includes a system configured to monitor the health of a tire. The system can include an inertial measurement unit (IMU). The IMU can be adhered or attached within a tire and/or to a wheel (e.g., a hub) and can measure linear accelerations and angular velocities associated with the wheel. The system can analyze the data measured by the IMU to determine various measures of tire health. For example, the system can determine an estimated tread depth of the tire, as well as qualities associated with the contact patch, toe, and/or camber of the tire and/or corresponding wheel. The system can provide alerts to a computing device (e.g., a user's mobile device) indicating various qualities associated with the tire and/or vehicle, such as a measured use of the tire (e.g., service time, distance traveled), a determined health of the tire, and/or various measurements, metrics, or calculations associated with the tire.
The disclosed technology includes a tire monitoring system that can comprise a tire sensor mounted within a tire and a computing device in communication with the tire sensor. The computing device can be configured to receive kinematic sensor data from the tire sensor and determine a contact patch angle based at least in part on the kinematic sensor data. The kinematic sensor data can be indicative of motion of the tire, and the contact patch angle being an angle that represents a contact patch associated with the tire. The computing device can be configured to determine an estimated tread depth of the tire based at least in part on the contact patch angle and, responsive to determining that the estimated tread depth of the tire is a below a tread depth threshold, output instructions to a user device associated with the tire monitoring system. The instructions can instruct the user device to provide an indication for one or more suggested actions.
The tire sensor can be attached to an inner liner of the tire.
The tire sensor can be attached to a wheel hub associated with the tire.
The tire monitoring system can be configured such that determining the contact patch angle can include determining when the tire sensor enters the contact patch and when the tire sensor exits the contact patch.
The tire monitoring system can be configured such that (i) determining when the tire sensor enters the contact patch includes determining a first time or an entry angle associated with the tire sensor transitioning from an arc-like path to a cord-like path and (ii) determining when the tire sensor exits the contact patch comprises determining a second time or an exit angle associated with the tire sensor transitioning from the cord-like path to the arc-like path.
The tire monitoring system can be configured such that (i) determining when the tire sensor enters the contact patch comprises determining a first time or an entry angle associated with the kinematic sensor data passing a first kinematic data threshold and (ii) determining when the tire sensor exits the contact patch comprises determining a second time or an exit angle associated with the kinematic sensor data passing a second kinematic data threshold.
The computing device can be configured to receive tire data indicative of a model of the tire.
The one or more suggested actions can include instructions to rotate the tire with other tires of a vehicle associated with the tire, instructions to align the tire and the other tires, instructions to inflate the tire, and/or instructions to replace the tire.
The monitoring system of claim 1, wherein the computing device is configured to determine the estimated tread depth only during periods in which the contact patch angle remains approximately constant during successive rotations of the tire.
The tire monitoring system can include a pressure sensor mounted inside the tire, and the pressure sensor can be configured to measure a pressure of the tire. The pressure sensor can be in communication with the computing device, and the computing device can be configured to receive, from the pressure sensor, pressure data that is indicative of the pressure of the tire and determine the estimated tread depth of the tire based at least in part on the contact patch angle and the pressure data.
The disclosed technology includes a method that can include receiving kinematic sensor data from a tire sensor, and the kinematic sensor data can be indicative of motion of a tire associated with the tire sensor. The method can include determining, based on the kinematic sensor data, a contact patch size associated with a contact patch of the tire and/or determining, based on the kinematic sensor data, a rotation rate of the tire. The method can include determining an estimated tread depth of the tire based at least in part on the contact patch size and/or the rotation rate and, responsive to determining that the estimated tread depth of the tire is a below a tread depth threshold, outputting instructions to a user device associated with the tire. The instructions can instruct the user device to provide an indication for one or more suggested actions.
Determining the contact patch size can include determining a contact patch angle that is indicative of an angular distance between entry of the tire sensor into the contact patch and exit of the tire sensor out of the contact patch. The angular distance can be calculated with respect to a center of the tire.
The method can include determining the estimated tread depth only during periods in which the contact patch angle remains approximately constant during successive rotations of the tire.
Determining the rotation rate of the tire can include calculating, based on the kinematic sensor data, a peak angular velocity and a mean angular velocity and calculating a peak tire rotation rate ratio by dividing the peak angular velocity by the mean angular velocity.
Calculating the peak angular velocity can include extracting a plurality of peak angular velocities for each of a plurality rotations of the tire and averaging the plurality of peak angular velocities, and calculating the mean angular velocity can include extracting a plurality of mean angular velocities for each of the plurality rotations of the tire and averaging the plurality of mean angular velocities.
The method can include receiving pressure data from pressure sensor and determining the estimated tread depth of the tire based at least in part on the contact patch size and the pressure data. The pressure data can be indicative of a pressure of the tire.
The disclosed technology includes a non-transitory, computer-readable medium storing instructions that, when executed by one or more processors, can cause a system to receive kinematic sensor data from a tire sensor. The kinematic sensor data can be indicative of motion of a tire associated with the tire sensor. The instructions, when executed by one or more processors, can cause the system to determine a rotation rate of the tire based on the kinematic sensor data, determine an estimated tread depth of the tire based at least in part on the rotation rate, and, responsive to determining that the estimated tread depth of the tire is a below a tread depth threshold, output instructions to a user device associated with the tire. The instructions can instruct the user device to provide an indication for one or more suggested actions.
Determining the rotation rate of the tire can include (i) calculating, based on the kinematic sensor data, a peak angular velocity and a mean angular velocity associated with the motion of the tire and (ii) calculate a peak tire rotation rate ratio by dividing the peak angular velocity by the mean angular velocity.
Calculating the peak angular velocity can include extracting a plurality of peak angular velocities for each of a plurality rotations of the tire and averaging the plurality of peak angular velocities, and calculating the mean angular velocity can include extracting a plurality of mean angular velocities for each of the plurality rotations of the tire and averaging the plurality of mean angular velocities.
Determining the contact patch size can include determining a contact patch angle based at least in part on when the tire sensor enters the contact patch and when the tire sensor exits the contact patch.
Reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein:
Throughout this disclosure, the disclosed technology is described in relation to systems configured to monitor the health of a tire. But the disclosed technology is not so limited. For example, the disclosed technology can be effective in monitoring the health of multiple tires (e.g., all tires on a single vehicle or a fleet of vehicles), as well as providing alerts regarding when to rotate, adjust, and/or replace one or more tires.
The disclosed technology includes a system comprising a tire-mounted and/or wheel-mounted (e.g., mounted to the hub) inertial measurement unit (IMU), which can be configured to measure linear acceleration data and/or angular velocity data. The IMU can be configured to measure linear acceleration data and/or angular velocity data associated with the motion of a tire, and the system can be configured to determine various indicators of tire health based on the linear acceleration data and/or angular velocity data. The system can be configured to determine a rolling radius of the tire and/or a distance between the IMU radius of rotation and a rolling radius of the tire. The system can be configured to monitor changes in one or both of these distances over time, which can be indicative of tread wear over time. Accordingly, the system can be configured to monitor tread depth of a tire and/or monitor change in the tread depth over time. The system can be configured to provide alerts to a computing device, such as a user's mobile device, indicating a determined health of a tire, the measured use (e.g., service time, distance traveled) of a tire, as well as other metrics, and the system can also be configured to suggest actions to increase the overall safety and/or efficiency of a vehicle as it relates to a tire (e.g., rotate tires, align tires, inflate tires, replace tires). For example, the system can be configured to transmit one or more alerts to the user's mobile device or some other computing device.
Various aspects of the disclosed technology will be described more fully hereinafter with reference to the accompanying drawings. This disclosed technology can, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The components described hereinafter as making up various elements of the disclosed technology are intended to be illustrative and not restrictive. Many suitable components that would perform the same or similar functions as components described herein are intended to be embraced within the scope of the disclosed electronic devices and methods. Such other components not described herein may include, but are not limited to, for example, components developed after development of the disclosed technology.
In the following description, numerous specific details are set forth. But it is to be understood that embodiments of the disclosed technology can be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail in order not to obscure an understanding of this description. References to “one embodiment,” “an embodiment,” “example embodiment,” “some embodiments,” “certain embodiments,” “various embodiments,” etc., indicate that the embodiment(s) of the disclosed technology so described can include a particular feature, structure, or characteristic, but not every embodiment necessarily includes the particular feature, structure, or characteristic. Further, repeated use of the phrase “in one embodiment” does not necessarily refer to the same embodiment, although it can.
Throughout the specification and the claims, the following terms take at least the meanings explicitly associated herein, unless the context clearly dictates otherwise. The term “or” is intended to mean an inclusive “or.” Further, the terms “a,” “an,” and “the” are intended to mean one or more unless specified otherwise or clear from the context to be directed to a singular form.
Unless otherwise specified, the use of the ordinal adjectives “first,” “second,” “third,” etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described should be in a given sequence, either temporally, spatially, in ranking, or in any other manner.
The disclosed technology relates to a system for monitoring the health of a tire. The system can include an IMU adhered (e.g., by tape, glue, epoxy, or something other adhesive) or otherwise attached within a tire and/or to a wheel. For example, the IMU can be adhered to the inner liner of a tire, the wheel rim, or the wheel hub. The IMU can be configured to detect and measure inertial data. The IMU can be configured to detect and measure linear accelerations and angular velocities associated with the tire in which the IMU is mounted. The system can be configured to determine, based at least in part on the linear acceleration data and the angular velocity data, changes in the distance between the IMU and the outer rolling surface. As will be appreciated, the difference in distance between the IMU and the outer rolling surface of the tire will decrease with tread wear (i.e., as the tread depth of the tire decreases). Accordingly, the system can be configured to monitor change in the tread depth over time. The system can be configured to measure other data, quantities, and aspects associated with the tire. Various aspects and functionalities of the disclosed technology are discussed more fully below.
An example computing device 200 configured to implement the system 100 is shown in more detail in
The controller 210 can include one or more of an application specific integrated circuit (ASIC), programmable logic device, microprocessor, microcontroller, digital signal processor, co-processor or the like or combinations thereof capable of executing stored instructions and operating upon stored data. The memory can include one or more suitable types of memory (e.g., volatile or non-volatile memory, random access memory (RAM), read only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, flash memory, a redundant array of independent disks (RAID), and the like) for storing files including operating system, application programs (including, for example, a web browser application, a widget or gadget engine, and or other applications, as necessary), executable instructions and data. The controller 210 can include a secure microcontroller, which can be configured to transmit and/or facilitate secure lines of communication. As will be appreciated, some or all of the processing techniques described herein can be implemented as a combination of executable instructions and data within the memory.
The controller 210 can be one or more known processing devices, such as a microprocessor from the Pentium™ family manufactured by Intel™, the Turion™ family manufactured by AMDυ, or the Cortex™ family or SecurCore™ manufactured by ARIVI™. The controller 210 can constitute a single-core or multiple-core processor that executes parallel processes simultaneously. For example, the controller 210 can be a single core processor that is configured with virtual processing technologies. The controller 210 can use logical processors to simultaneously execute and control multiple processes. The controller 210 can implement virtual machine technologies, or other similar known technologies to provide the ability to execute, control, run, manipulate, store, etc. multiple software processes, applications, programs, etc. One of ordinary skill in the art would understand that other types of processor arrangements could be implemented that provide for the capabilities disclosed herein.
The computing device 200 can include one or more storage devices 234 configured to store information used by a controller 210 (or other components) to perform certain functions related to the disclosed technology. As an example, the computing device 200 can include memory 230 that includes instructions to enable controller 210 to execute one or more applications, network communication processes, and any other type of application or software known to be available on computer systems. Alternatively, the instructions, application programs, etc. can be stored in an external storage or available from a memory over a network. The one or more storage devices can be a volatile or non-volatile, magnetic, semiconductor, tape, optical, removable, non-removable, or other type of storage device or tangible computer-readable medium.
The computing device 200 can include memory 230 that includes instructions that, when executed by the controller 210, cause the computing device 200 to perform one or more processes consistent with the functionalities disclosed herein. Methods, systems, and articles of manufacture consistent with the disclosed technology are not limited to separate programs or computers configured to perform dedicated tasks.
The memory 230 can include one or more memory devices that store data and instructions used to perform one or more features of the disclosed technology. The memory 230 can also include any combination of one or more databases controlled by memory controller devices (e.g., one or more servers, etc.) or software, such as document management systems, Microsoft™ SQL databases, SharePoint™ databases, Oracle™ databases, Sybase databases, or other relational databases. The memory 230 can include software components that, when executed by the controller 210, cause the computing device 200 to perform one or more processes consistent with the disclosed technology. The memory 230 can include a memory module consistent with the disclosed technology.
The computing device 200 can also be communicatively connected to one or more memory devices (e.g., databases (not shown)) locally or through a network. The remote memory devices can be configured to store information and can be accessed and/or managed by the computing device 200. By way of example, the remote memory devices can be document management systems, Microsoft™ SQL database, SharePoint™ databases, Oracle™ databases, Sybase™ databases, or other relational databases. Systems and methods consistent with disclosed technology, however, are not limited to separate databases or even to the use of a database.
The computing device 200 can include any number of hardware and/or software applications that are executed to facilitate any of the operations. The one or more I/O interfaces can be utilized to receive or collect data and/or user instructions from a wide variety of input devices. Received data can be processed by one or more computer processors as desired in various implementations of the disclosed technology and/or stored in one or more memory devices.
As will be appreciated, the IMU 104 can be mounted at a position having a radius ρ within the perfectly circular tire 102 of outer radius r rolling at angular speed {dot over (θ)}(t). The IMU 104 can experience a centripetal acceleration by virtue of the IMU 104 rotating within the tire 102 at angular speed {circumflex over (θ)}(t) at radius ρ. If the tire 102 rolls with rotational velocity {dot over (θ)}(t) and accelerates with rotational acceleration {umlaut over (θ)}(t), the IMU 104 can also experience a linear acceleration associated with the forward acceleration αroll of the tire 102. If the tire 102 slips negligibly against the road or ground as it rolls, then αroll=r{umlaut over (θ)}(t). As will be appreciated, the amplitude of the linear acceleration can be sinusoidally modulated as the IMU 104 rotates in and out of alignment with the forward motion of the tire 102 (in instances where the tire 102 is traveling forward) along the ground.
Accordingly, the system 100 can be configured to determine a “rolling radius” of the tire 102 based on the dynamics of an accelerating tire 102. That is, for an accelerating tire 102, the system 100 can sense the outer radius r based, at least in part, on the detected translational and rotational accelerations, and based on the principle that the radius r of the tire 102 will decrease as the tire 102 wears and tread depth decreases, the system 100 can determine the tread depth of the tire 102. To determine the tread depth value, the system 100 can compute the ratio of the translational and rotational accelerations to determine the radius r of the tire 102 at any time t. Alternatively, the system 100 can integrate the detected accelerations over some time interval (e.g., some predetermined time interval, some random time interval) to determine changes in translational velocity and rotational velocity and can determine a ratio of the translational and rotational velocities. Alternatively, the system 100 can twice integrate the accelerations to obtain translational and rotational displacements and can determine a ratio of the translational and rotational velocities:
While the IMU 104 may not measure αroll(t) directly, one of skill in the art will understand that the system 100 can be configured to derive this value from the accelerations that the IMU 104 does directly measure, namely αr(t) and aθ(t). For example, the system 100 can be configured to determine αroll(t) using Equation 2 or Equation 3:
where g is the acceleration due to gravity. As will be appreciated, the three ratios shown in Equation 1 are equivalent in an idealized model (e.g., as depicted in
As will be appreciated the above computations can be appropriate for a perfectly round and rigid tire, but in the case of a perfectly round, flexible tire, the size (e.g., radius r) of the tire 102 can change with inflation pressure. Accordingly, the system 100 can be configured to determines tread depth in a differential manner using measurements acquired from the IMU 104. Accordingly, the system 100 can be configured to measure the difference δ between the outer radius r of the tire 102 and the IMU radius ρ:
δ=r−ρ (4)
The IMU radius ρ is defined by the position at which the IMU 104 is mounted within the tire 102, and the IMU 104 can be mounted at any radius ρ. For example, the IMU 104 can be mounted on the wheel hub or the tire inner liner. The system 100 can be configured to compute the IMU radius ρ from the centripetal acceleration of the IMU 104 described above, for example.
To illustrate a possible method of determining δ, it can be helpful to consider a situation in which the IMU 104 is at its highest point (i.e., directly above the center of the tire 102) such that θ(t)=2πn for some integer n. In this case, the IMU 104 can report the acceleration components shown in Equations 5 and 6:
αr(t)=g−ρ{dot over (θ)}2 (5)
and
αθ(t)=(ρ+r){umlaut over (θ)} (6)
Equation 5 indicates that the IMU's 104 radial (vertical) accelerometer registers g in the upward direction. (Because the IMU's 104 accelerometers measure the force necessary to keep a small proof mass stationary with respect to the IMU's 104 body, the component of the total force measured by the IMU 104 that opposes the force of gravity points upward.) Because the IMU 104 is at its highest point on the tire, the instantaneous centripetal acceleration p{dot over (θ)}2 registers in the downward direction. As can be seen this result does not involve the outer radius r, but the outer radius r does appear in Equation 6. Equation 6 indicates that the IMU's 104 tangential (horizontal) accelerometer registers the sum of two terms: the first term due to rotational acceleration and the second term equal to the tire's translational acceleration r{umlaut over (θ)}(t). Thus, for a perfect IMU 104 having no bias and no noise in its data and at an instant at which θ=2πn, αr, αθ, {dot over (θ)}, and {umlaut over (θ)} can be sampled at that instant and Equations 5 and 6 can be used to compute:
Equations 7 and 8 can in turn be used tom compute the distance between the IMU 104 and the outer tread surface:
The system 100 can be configured to incorporate many IMU 104 samples into each measurement by, for example, basing the calculations on the output of a well-designed state estimator for θ and {dot over (θ)}, which can help address the noise present in a realistic IMU 104.
Referring to
r(θ)=r0 (10)
and
ρ(θ)=ρ0 (11)
where r0 and ρ0 are constants.
In order for the tire 102 to take on the flattened shape of the contact patch 306, the tread of the tire 102 must bunch up as it enters the patch and then relax as it exits the patch. This gives rise to an effective “rolling radius” that may not be equal to either the loaded radius rπ or unloaded radius r0 of the tire.
The rolling radius of the tire 102 can be defined as the ratio of the lateral road speed of the tire 102 to the angular speed of the tire 102:
As shown in
Alternatively, the computing device 200 can be configured to compute the differential for a flattened tire as:
δ′≡rroll−ρ0 (13)
While δ′may not correspond to any physically extensive quantity at a particular angular location (in that rroll exists within the contact patch 306 and ρ0 exists outside the contact patch 306), monitoring the difference between them can still provide an effective approach to offsetting the effects of inflation pressure and vehicle loading on the individual quantities. Alternately, the computing device 200 can be configured to estimate the specific differential
δπ=rπ−ρπ≈rroll−ρπ (14)
where ρπ≡ρ(π), which is the IMU radius ρ when the IMU 104 is at its lowest point (i.e., directly below the center of the tire 102).
Equations 5 and 6 give components of the acceleration experienced by the IMU 104 at particular isolated time instants only. Corresponding expressions valid for all times at which θ lies outside the contact patch 306 and the associated transition regions are:
αr(t)=rroll sin θ(t){umlaut over (θ)}(t)−ρ0{dot over (θ)}(t)2+g cos θ(t) (15)
and
αθ(t)=[rroll cos θ(t)+ρ0]{umlaut over (θ)}(t)−g sin θ(t) (16)
While the IMU angle θ is in and immediately adjacent to the contact patch 306, the IMU's 104 outputs may no longer reflect αr, αθ, {dot over (θ)} as depicted in
The computing device 200 can be configured to use Equations 15, 16, and/or a suitably constructed state estimator to extract the rolling radius rroll and IMU radius ρ0 to compute the differential δ′. As noted above, computing δπ requires additional modeling to determine ρπ, which is not the same as ρ0. To compute δπ, the computing device 200 can be configured to use Equations 15 and 16 and an accurate estimator for the IMU angle θ to determine the vertical acceleration αz of the IMU 104 as a function of time and subsequently double integrate the vertical acceleration αz as the IMU 104 moves from its apex (θ=2πn) to the point where it starts to enter the contact patch 306 (and Equations 15 and 16 begin to fail). This can indicate the change in height of the IMU 104 as it rolls around the axle, and since the height is ρ0+ρπ, the computing device 200 can be configured to determine an approximation for ρπ.
Alternatively, the computing device 200 can be configured to determine ρπ based on the IMU's 104 outputs to detect the angle θp subtended by the contact patch 306, and the computing device 200 can be configured to then compute:
ρπ=ρ0 cos(θp/2) (17)
Because all outputs from the IMU 104 ideally go to known constants when the IMU 104 enters the contact patch 306, the computing device 200 can be configured to determine when the IMU 104 is in the contact patch 306. The computing device 200 can also be configured to measure {dot over (θ)}in and {dot over (θ)}out just before the IMU 104 enters the contact patch 306 and just after the IMU 104 exits the contact patch 306. The computing device 200 can be configured to subsequently calculate
θp≈Δt({dot over (θ)}in+{dot over (θ)}out)/2 (18)
where Δt is the time the IMU 104 spends in the contact patch 306. Alternatively or in addition, the system 100 can include a second IMU 104. For example, the second IMU 104 can be positioned directly opposite the first IMU 104 with respect to the center of the tire 102, which may increase or maximize the amount of useful data by ensuring that at least one IMU 104 will always be outside the contact patch 306. This may provide a better estimate of {dot over (θ)}.
Equations 15 and 16 describe the acceleration components experienced by an IMU 104 that is physically aligned with the equatorial plane of a tire 102 that is itself aligned with respect to the direction of rolling. The more general situation of a misaligned IMU 104 and a misaligned tire 102 rolling in a fixed direction can be described as follows. First, let u be a constant unit vector that points along the axis of rotation of the tire 102 in a right-hand sense. Then,
where ex and ez are as defined in
The instantaneous displacement of the IMU 104 from its center of rotation can now be written as Ru(θ(t))(ρ0{tilde over (e)}r), where Ru(φ) is an orthogonal matrix that rotates any vector it left-multiplies by an angle φ in a right-handed sense about the axis defined by u. (Thus the IMU's 104 displacement passes through the “top dead center” value ρ0{tilde over (e)}r each time θ(t) passes through a multiple of 2π.) The above definitions can be used to generalize Equations 15 and 16 for the accelerations sensed by the IMU 104's accelerometers to
αi=[Ru(θ(t))A{tilde over (e)}i]·[rroll sec τ {umlaut over (θ)}(t)+gez+ρ0Ru(θ(t)){tilde over (e)}r] (23)
where i represents θ, u, or r, and where A is a constant orthogonal matrix that characterizes the misalignment of the IMU relative to the tire. Similarly the angular rates sensed by the IMU's gyroscopes can be written as
ωi=[Ru(θ(t))G{tilde over (e)}i]·u{dot over (θ)}(t) (24)
where i represents θ, u, or r, and where G is a constant orthogonal matrix that characterizes the misalignment of the IMU 104 relative to the tire 102. One skilled in the art will appreciate that the accelerations and angular rates reported by a real IMU 104 may not be exactly as predicted by Equations 23 and 24 but may include contributions from imperfections such as bias and noise. It will also be appreciated that Equations 23 and 24 can be written in many equivalent forms, including forms chosen to be convenient for efficient computation.
As will be appreciated, as the tire 102 comes to a stop, the computing device 200 can be configured to use the temporarily constant components of the gravitation constant gez as measured by the IMU's 104 accelerometers to determine the IMU's 104 orientation. Thus, the computing device 200 can then have a θ(t0) to integrate from as the tire 102 accelerates away from the stopped position. Such known-stationary states can permit the computing device 200 to measure and calibrate out IMU biases, which may tend to be significant and may drift unpredictably over time. The computing device 200 can be configured to reduce or minimize such errors by limiting how long measurements are taken by the IMU between bias nullings performed by the computing device 200 (e.g., at stop points of the tire 102). Thus, the computing device can be configured to determine the vehicle is coming to a stop, null out any gyro biases of the IMU, determine θ(t0) based on data from the IMU's 104 accelerometers, determine the vehicle is beginning to accelerate, sample the IMU 104 rapidly for a brief interval (e.g., one revolution of the tire), and process the results to produce a tread measurement.
As described herein, changes in the rolling radius of a tire 102 can correspond to changes in tread depth of the tire 102, and the pressure, temperature and/or load on the tire can affect the rolling radius of a tire 102. To increase the overall accuracy of the system 100, the system 100 can include one or more pressure sensors configured to detect and/or monitor the internal pressure of the tire 102, and/or the system can include one or more temperature sensors configured to detect and/or monitor the temperature of the tire 102. Alternately, the system 100 can include a geolocation sensor and can be configured to look up the local temperature from, for example, a third-party weather service to estimate a temperature of the tires 102. Furthermore, as discussed herein, the differential approach to determining the tread depth of the tire 102 can decrease the impact of varying pressure on the tread depth calculation.
While it is currently difficult to determine vehicle load directly (e.g., weight of the vehicle, passengers, and cargo), the impact of the load variable can be overcome by aggregating IMU data and determining an estimated tread depth based on large, aggregated trends of data. That is, the computing device 200 can be configured to evaluate whether the rolling radius is decreasing over time, which can be indicative of the tread depth decreasing over time. Furthermore, as discussed herein, the differential approach to determining the tread depth of the tire 102 can decrease the impact of varying vehicle load on the tread depth calculation.
The system 100 can be configured to measure the change in tread depth over time. For example, the system 100 can be configured to measure or estimate a decrease in a tire's 102 rolling radius over time and can determine a corresponding decrease in the tire's 102 tread depth by, for example, applying the system and any of the methods described herein. The system 100 can be configured to receive an indication of the model of tire installed on a vehicle so as to determine a starting tread depth of the tire 102, or the system 100 can be configured to receive one or more measurement values associated with the starting tread depth of a tire 102 installed on a vehicle. The system 100 can assign a default tread depth for a new tire 102 (e.g., 10/32″, 11/32″). The system 100 can assign a default tread depth for a new tire 102 unless different values or other information corresponding to the new tire 102 is provided (e.g., a measured tread depth or a make/model of the tire). As time progresses and the system 100 monitors and determines a decrease in the tread depth of the tire, the system 100 can be configured to receive one or more measurement inputs associated with a measured tread depth of the tire 102. These one or more measurement inputs can be used by the system 100 to validate, correct, and/or update the current tread depth of the tire 102 according to the system.
Alternately or in addition, the system 100 can be configured to measure the actual tread depth of a tire 102 by, for example, applying the system and methods described herein. Such a configuration may require more precise measurements by the IMU 104 and/or other sensors (e.g., as compared to determining a decrease in tread depth over time), but such a configuration can be configured to measure the actual tread depth of the tire 102 without requiring a starting tread depth to be inputted into the system 100.
Alternatively or in addition, the system 100 can be configured to determine an extent of the contact patch 306 of the tire based on measurements from the IMU 104. For example, the system 100 can be configured to determine the angular extent of the contact patch 306.
Alternatively or in addition, the computing device 200 can be configured to detect relatively quiescent periods of time in which the an IMU 104 adhered to the inner liner of the tire 102 is essentially stationary relative to the ground as it traverses through the contact patch 306. Specifically, the computing device can detect such periods by locating relatively constant values of linear accelerations and angular velocities within the IMU measurements.
The computing device 200 can use any of several measures to quantify the extent of the contact patch 306.
to—time near zero (less than half mean angular velocity);
tp—time between peaks on either side of dip in angular velocity;
t20—time spent more than 20% above mean angular velocity;
t10—time spent more than 10% above mean angular velocity; and
peak—ratio of peak angular velocity to mean angular velocity.
Consistent with the methodologies described herein, the angle subtended by the contact patch 306 at the axle associated with the tire 102 can be referred to as the contact patch angle θp (see
As an illustrative example,
As tread depth decreases over the life of a tire 102, certain aspects and features of the tire 102 change, and changes in these aspects or features can be used to determine or approximate the tread depth of the tire 102. The relationships between tread depth wear and changes in these aspects or features can be specific to each tire model. Thus, a tread depth estimation model can be constructed for a given tire model, and the tread depth estimation for that tire model need not be altered or replaced unless a manufacturing change or some other change occurs that results in different deformation characteristics of the tire model.
For example, as tread depth decreases, the size and shape of the contact patch 306 changes. More specifically, the width of the contact patch 306 (which can be expressed as θp) can change as tread depth decreases. Typically, the width of the contact patch 306 will decrease as the tread depth decreases, although for some models of tire, the width of the contact patch 306 may increase as the tread depth decreases. Regardless, it is possible to associate changes in the width of the contact patch 306 with decreases in tread depth, as discussed herein. As a related example, as tread depth changes, the tilt angle, speed, and other aspects of the tire 102 (and the liner of the tire 102) within the contact patch 306 can also change.
Multiple methods or models can be employed to determine the contact patch angle θp. For example, the contact patch angle θp can be determined based on entry instant tin and exit instants tout. A first method, Method 1, can include constructing a wheel rotation model (e.g., implementing some or all of Equations 15, 16, and 19-24), determining the angles θin and θout that correspond to tin and tout, respectively, and computing the contact patch angle θp as the contact patch exit angle θout less the contact patch entry angle θin. For example, a state estimator (e.g., Kalman filter, regression analyzer) can be configured to determine the contact patch angle θp.
Because a tire angle θ can be associated with every time instant t, the IMU data can be expressed as one or more functions of θ rather than t. This in turn allows normalized versions of multiple contact patch waveforms (corresponding to respective types of IMU data) to be aligned with one another and coherently averaged in order to reduce the effects of random noise. This normalization can be performed even if the different contact patch waveforms were sampled at different wheel rotation rates co. It can be useful to perform the normalizations such that the results are approximately independent of ω. For example, a suitable normalization for gyroscope rates can be performed by dividing the gyroscope rate data ω.
Another example method, Method 2, involves estimating the tire rotation rate ω by averaging tire rotation rates ωgyro sampled from gyroscope data at times (or angles) well removed from the contact patch 306 and calculating ω(tout−tin) to determine the contact patch angle θp. Any misalignment of the IMU 104's gyroscope axes with the tire 102 can be circumvented or minimized by computing the Euclidean magnitude of the three rate components before averaging:
In addition or alternatively, values of θpfrom multiple contact patch traversals can be averaged to reduce the effects of random noise.
Another example method, Method 3, involves estimating the rotation rate ω of the tire 102 by dividing 2π radians by the average time between successive contact patches 306 and computing: θp=ω(tout−tin). In addition or alternatively, values of θpfrom multiple contact patch traversals can be averaged to reduce the effects of random noise.
Yet another example method, Method 4, involves partitioning all IMU data into a first group for data obtained inside contact patches (i.e., between tin and tout for any contact patch 306) and a second group for data obtained outside contact patches over one or more complete rotations (e.g., as determined using successive tin instants). The partitioning can be performed after the data has been collected or while sampling from the IMU 104 (e.g., receiving data from the IMU 104), and the sampling can be performed at a constant rate. Corresponding sample counts Nin and Nout can be used to compute θp=2πNin/Nout. It will be appreciated that Method 4 can be equivalent to Method 3 but does not explicitly reference time or rate values.
These and any other such methods can provide differing balances of accurate results and computational efficiency. For example, Method 1 can typically produce the most accurate results, particularly under acceleration conditions of the tire 102, but Method 1 also requires the most computational power of these example methods. Methods 2, 3, and 4 are typically less computationally expensive than Method 1, and Methods 3 and 4 generally provide the added benefits of being insensitive to both sample rate (assuming it is essentially constant) and IMU scale calibration. To limit errors due to acceleration when using Methods 2 through 4, it can be helpful to repeatedly measure the time interval (or number of samples) between successive contact patches 306 (e.g., measuring successive tin instants) and evaluate estimated tread depth only during periods (i.e., stretches of successive contact patches 306) in which this interval stays relatively constant (e.g., below a predetermined amount of variation or deviation from an average tin instant). Regardless of the method used, it can be beneficial to perform lowpass filtering of IMU data before use, which can help provide more accurate results.
In addition or alternatively, a peak tire rotation rate ratio rpeak (illustrated in
Both the contact patch angle θp and the peak tire rotation rate ratio rpeak can typically depend on tire pressure and wheel load, in addition to tread depth. Specifically, both of these features tend to increase with decreasing pressure. Accordingly, it can be helpful to incorporate a pressure sensor (e.g., into the IMU sensor 104, although a pressure sensor separate from the IMU sensor 104 can be used) and to include pressure dependence in the tire-model-specific models relating the contact patch angle θp and the peak tire rotation rate ration rpeak to tread depth changes. The outcome of the characterization for each tire model is then a function that maps the contact patch angle θp to tread depth and/or the contact patch angle rpeak to tread depth, as well as the and pressure to tread depth. For illustrative purposes only,
If wheel load is desired to be included in the model(s), load data from a load cell or another sensor configured to measure load, pressure, and/or force (e.g., as discussed more fully below) can be used. Alternatively, a backend analysis can be performed to compute (e.g., by the system 100) nominal tread depths without regard to load and a history of the results can be maintained (e.g., by the system 100) such that historical data detailing load over time is created. Because vehicle load, and therefore wheel or tire load, typically increases and decreases over time within a limited range, the system 100 can analyze the history of computed nominal tread depths to determine a long-term trend or relationship between the computed nominal tread depths and the corresponding real tread depth decrease. As a simple example, measurements made when a vehicle is minimally loaded typically produce the smallest nominal tread depth values (when load dependence is omitted from the computation), so an accurate tread depth trend can be obtained from just the values at the local minima, or valleys, of the nominal tread depth history.
In addition or alternatively, load changes can be estimated by exploiting differences in the way different features like the contact patch angle θp and the peak tire rotation rate ration rpeak depend on load. If their load dependences of the contact patch angle θp and the peak tire rotation rate ration rpeak are sufficiently different (which is the case for at least some tire models), to the system 100 can construct a function or model that maps multiple feature values (e.g., data indicative of the contact patch angle θp and/or data indicative of the peak tire rotation rate ration rpeak) and pressure data to a unique tread depth.
Regardless of how load changes are accounted for over the life of a tire 102, there can still be an overall load dependence due to the vehicle's unloaded weight. That is, different types of vehicle can have different unloaded vehicle weights (i.e., the weight of the vehicle itself), which may cause the sensor to produce different feature values (e.g., acceleration, rotation rate, contact patch angle θp, peak tire rotation rate ration rpeak) even if all vehicles have the same type of tire and have the same amount of extra weight added to the respective vehicles. This variation can be reduced or minimized by, at the time of sensor installation, recording the initial tread depth (e.g., in the system 100). As an example, this process can be automated when sensors are installed in new tires under the assumption that all new tires of a given tire model will have the same initial tread depth upon installation (when installed as a new, previously unused tire). The initial tread depth can be used as a calibration point. That is, upon installation of a new tire 102, the IMU 104 and/or system 100 can determine a contact patch angle of the new tire 102 and a pressure of the new tire 102. Based on the processes and methodologies described herein in combination with the known tread depth and/or pressure of the new tire 102, the IMU 104 and/or system 100 can determine the load on the tire 102 at installation. As an example, a heavy vehicle and a light vehicle can both have a new tire 102 of the same model installed, and either vehicle will produce a different patch angle, which can be used to determine information about the vehicle weight through the determined tire load.
Referring to
The computing device 200 can be configured to estimate or determine one or more state variables based on consecutive measurements from the sensor(s) within a predetermined amount of time or a predetermined number of events (e.g., a predetermined number of tire rotations). Each state variable update (e.g., successive sensor data) can correspond to an observation window rather than a single measurement. Successive observation windows can be widely separated in time. This can save power, which is particularly useful if the sensor(s) are battery-powered. Alternately or in addition, this can enable the computing device 200 to select only observation windows (e.g., sensor data corresponding to particular times, positions, or rotation angles) at which it is easier to analyze the tire motion. For example, the computing device 200 can be configured to select only observation windows in which the vehicle is moving slowly but accelerating significantly. As another example, the computing device can be configured to select only observation windows in which the sensor (e.g., IMU 104) is moving through the contact patch 306 and/or the tire 102 is not accelerating (i.e., the tire 102 has an acceleration (e.g., horizontal, angular) that is zero or substantially close to zero).
As depicted in
The system can include an outlier detection module (e.g., as denoted by box 1004 in
Referring to
Referring to
Alternately, referring to
In the event the feedback of prior estimations is incorrect and erroneously influences updated estimations (e.g., if the observation window occurs at a time when the vehicle's motion is not well described by the underlying physical model), block 606, which is labeled “Retrospective Evaluation,” can represent logic applied by the computing device 200. The Retrospective Evaluation logic can be configured to detect bad updates (e.g., erroneous data) and prevent the bad updates from contaminating the state estimator. As will be appreciated the trend and change analysis can be configured to improve the accuracy of generated state variable estimates, which can improve the accuracy of the state estimator by feeding improved estimates into the state estimator together with its own prior estimations.
While the preceding disclosure has focused largely on determining a tread depth of the tire 102, the system 100 can be configured to provide alternate functionalities. For example, the system 100 can be configured to detect, via the IMU 104 or another sensor, the number of rotations of the tire 102 and/or the actual distance traveled by the tire 102. As another example, the system 100 can be configured to detect, via the IMU 104 or another sensor, the size of the contact patch 306 of the tire 102 as described in more detail above. The size of the contact patch 306 can be indicative of the tire pressure and/or load experienced by the tire 102. For example, a contact patch 306 above a predetermined size can be indicative of a low tire pressure and/or a high load being exerted on the tire 102. Either scenario can increase wear of the tire 102 and may decrease the useful life of the tire 102.
The system 100 can be configured to use the determined size of the contact patch 306 to improve the accuracy of the tread wear calculation. For example, the computing device 200 can be configured to compute a vehicle load based on the determined contact patch 306 size and a pressure measurement of the tire 102. An estimate of the vehicle load, combined with the pressure measurement, can be used to address the dependency of rolling radius on inflation pressure and vehicle load described above.
The system 100 can be configured to more directly determine the load experienced by a tire 102, which can increase the accuracy of the determined size of the contact patch 306, which can in turn increase the accuracy of the determined rolling radius, tread depth, and/or other metrics. The system 100 can include one or more load sensors configured to determine the load experienced at or near one or more tires 102. For example, the system 100 can include a load cell or another sensor configured to measure load, pressure, and/or force. The load sensor can be installed at or near an axle, a vehicle hub, a wheel hub, or any other location on a vehicle that can be useful for determining the load experienced by a tire 102. As a more specific example, one or more load sensors can be located proximate one, some, or all of the wheel hub bolts that attach a wheel to a vehicle, which can provide detailed information regarding the load experienced by the corresponding tire 102. The load sensor can be configured to communicate (e.g., wirelessly) with the system 100.
The system 100 can be configured to determine load indirectly via one or more non-load sensors. For example, the system 100 can be configured to determine, based on data from the IMU 104 (e.g., immediately upon the tire 102 accelerating from a stopped position and/or immediately preceding the tire 102 reaching a stopped position) the size of the contact patch 306, and the system can be configured to determine, based on the contact patch 306 determination and pressure data from a pressure sensor measuring air pressure of the tire 102, an estimated load of the tire 102.
Load measurements and/or determinations can provide an added measure of safety for the commercial trucking industry, for example, as these tire-specific determinations can provide an indication of relative loading. This can in turn enable customized adjustment of tire pressure for specific hauling vehicles and/or specific tires of a given hauling vehicle based on determined load balances and tire placements.
The system 100 can be configured to detect, via the IMU 104, the alignment (e.g., toe and/or camber) of one or more tires on a vehicle. For example, the IMU 104 can be configured to provide a real-time or near real-time determination of a sudden change in camber. If the computing device 200 does determine that the camber and/or toe has undergone a sudden change, the computing device 200 can assume that the alignment of the tire has become misaligned. The system 100 can include an automatic alignment system configured to automatically return a misaligned tire (e.g., a tire with incorrect camber and/or incorrect toe) to an aligned configuration. The automatic alignment system can include one or more actuators attached to the chassis, axle, wheel hub, or another component of the vehicle. The automatic alignment system can be configured to tilt, rotate, and/or shift a wheel to return the tire to an aligned configuration. The amount of tilt, rotation, and/or shift provided by the automatic alignment system can be determined by the severity of misalignment calculated or otherwise detected by the computing device 200. Also, the system 100 can provide dynamic adjustments in alignment to permit different characteristics that the alignment factors provide in different situations.
The system 100 can be configured to provide alerts and tire-health-related information to a user device. As discussed herein, the computing device 200 can serve as a user device. Alternately, the computing device 200 can be included in the system 100, and the computing device can be configured to transmit alerts to a user device (e.g., via a mobile network, the internet, RFID, Bluetooth, or some other communication method or functionality). Regardless, the system 100 can be configured to provide alerts to a user, and the alerts can be indicative of alignment or misalignment of one or more tires (e.g., toe, camber, or caster), inflation pressure (e.g. underinflation) of one or more tires, tread depth of one or more tires, temperature of one or more tires, tire rotation recommendations, tire life (e.g., time installed on vehicle, distance traveled), remaining tire life estimates, tire replacement recommendations, or any other useful information. Possible applications of the aggregated data can include providing alerts to retailers and/or manufactures (e.g., alerts regarding performance, life characteristics, and other factors regarding one or more types of tires), fleet management including maintenance or replacement of tires and/or vehicles of a fleet of vehicles, and providing industry-wide data for industry analysts.
While the disclosed technology has been described in connection with what is presently considered to be the most practical embodiments, it is to be understood that the disclosed technology is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
This application claims priority to U.S. Provisional Patent Application No. 62/795,363, filed on Jan. 22, 2019, which is incorporated herein by reference in its entirety as if fully set forth below.
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