FIELD

The present description relates generally to methods and systems for correcting a vehicle speedometer based on data obtained from a longitudinal acceleration sensor.

BACKGROUND/SUMMARY

Speedometers rely on sensors to measure a rotational speed of a vehicle driveshaft and/or vehicle wheels, which is converted to vehicle speed via relevant equations. In some examples, the sensor may be an existing anti-lock braking system (ABS) sensor that measures vehicle speed. In such an example, an ABS control unit may measure and average the input from wheel speed sensors to obtain vehicle wheel speed. Then, vehicle speed may be derived from the wheel speed, based on a known tire diameter. Similar logic applies to the use of driveshaft rotational speed sensors.

However, such speedometer systems may in some cases become inaccurate. As one example, a rolling radius of vehicle tires may change over time, thus impacting the accuracy of vehicle speed measurements. As other examples, vehicle operators may modify their vehicles by one or more of changing tire size, changing final drive ratio, purposely altering tire pressure, etc. In such examples, inaccurate vehicle speeds may be reported to a vehicle operator, and to any other electronic controllers that rely on vehicle speed for operation, which is of course undesirable.

U.S. Pat. No. 8,336,364 teaches a method for calibrating wheel speed signals from wheel speed sensors during vehicle acceleration/deceleration, by integrating signals of at least one longitudinal acceleration sensor to yield a vehicle speed, and comparing the vehicle speed against wheel speed signals of individual wheel rpm sensors. When a difference falls outside of a predetermined range, a parameterized tire circumference of the associated wheel is adaptively recalibrated until the difference falls within the predetermined range.

However, the inventors herein have recognized potential issues with the above-referenced application. Specifically, there is a lack of disclosure of how the acceleration and deceleration events are selected for use in obtaining vehicle speed based on signals integrated via the at least one longitudinal acceleration sensor, and the inventers have recognized that only very particular vehicle acceleration/deceleration events can reliably be used to obtain vehicle speed by integrating longitudinal acceleration sensor data. For example, U.S. Pat. No. 8,336,364 teaches that data from the longitudinal acceleration sensor is collected when an error due to an offset of the longitudinal acceleration sensor has been compensated for, but there is no disclosure as to how the offset is compensated for, or even what the offset pertains to or is due to. U.S. Pat. No. 8,336,364 also discloses using acceleration/deceleration events for which the vehicle is not traveling uphill or downhill, and for which acceleration values fall within certain limits (e.g., not too high or too low). However, the inventors have recognized that stack-up errors in the integration of longitudinal acceleration sensor data may render a high likelihood of error in the estimate of vehicle speed if appropriate reference points for vehicle acceleration/deceleration events are not used to clearly define acceleration/deceleration events that can be used for robust analysis. Errors in the estimate of vehicle speed may result in erroneous adaptive recalibration of tire circumference, which may further exacerbate the issue that the calibration process attempts to resolve.

Thus, the inventors herein have developed systems and methods to at least partially address the above-mentioned issues. In one example, a method comprises with a vehicle at a first reference point, commencing integrating signals of a longitudinal acceleration sensor to obtain a first vehicle velocity and obtaining a second vehicle velocity from a wheel speed sensor, stopping obtaining the first and the second vehicle velocity responsive to the vehicle reaching a second reference point, and updating a relevant vehicle parameter as a function of a difference between the first vehicle velocity and the second vehicle velocity. In this way, vehicle velocity as indicated based on wheel speed sensor(s) may be improved.

As one example of the method, the first reference point may include the vehicle just beginning to accelerate from a vehicle-stopped condition, for example as soon as a controller of the vehicle receives an indication that the vehicle is traveling at greater zero miles per hour. In such an example, the second reference point may include a condition where a speed of the vehicle is greater than a first speed but less than a second speed, and wherein the speed is reached at a time since commencing integrating the signals of the longitudinal acceleration sensor to obtain the first vehicle velocity and obtaining the second vehicle velocity that is greater than a first time duration but less than a second time duration.

As another example, the first reference point may include the vehicle traveling within a threshold of a predetermined non-zero vehicle speed. In such an example, the second reference point may include the vehicle coming to a complete stop after a third time duration but before a fourth time duration since the vehicle was traveling within the threshold of the predetermined non-zero vehicle speed.

As another example, the method may include discarding data pertaining to the first and the second vehicle velocity in response to acceleration or deceleration of the vehicle not being monotonic between an entirety of the first reference point and the second reference point.

As another example, the relevant vehicle parameter may be a tire diameter. Additionally or alternatively, the relevant vehicle parameter may be a final drive ratio.

As another example, updating the relevant vehicle parameter may include changing the relevant vehicle parameter when a difference between a first slope of the first vehicle velocity between the first and the second reference points differs from a second slope of the second vehicle velocity between the first and the second reference points by more than a threshold difference. In such an example, the method may include maintaining the relevant vehicle parameter unchanged when the difference is less than the threshold difference.

As yet another example, the method may further comprise an indication that a steering wheel of the vehicle is maintained within a predetermined steering wheel angular range between the first reference point and the second reference point. Furthermore, the method may include an indication that a surface upon which the vehicle is traversing between the first reference point and the second reference point is within a predetermined threshold angle of a perfectly level surface.

The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.

It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.

