Let the Apple Car rumors continue to roll on. Apple has been granted a patent (number 10,247,816) for an “apparatus and method to measure slip and velocity” on an automobile. The goal is to improve skid recovery and implement automatic safety systems for autonomous vehicles.
In the patent filing, Apple notes that vehicles use tires that are compliant air-filled structures that exert force on the road by continually deforming and slipping relative to the road. For road vehicle stability and traction, modern vehicle control systems often use an estimate of how the vehicle moves with respect to the road.
Accurately estimating road-relative velocity vectors is of particular importance as velocity can be used for feedback control, position estimation, detection, and intelligent response to tire nonlinearities and sliding. However, Apple says that because of the compliance of the tires, directional stiffness, the radius of the tire, among other things, can vary as well as various factors such as temperature, pressure, wear, and load from the car and road, can make conventional approaches to velocity estimation challenging.
In response, safety systems have been developed that can determine the road-relative velocity using wheel encoders, inertial sensors, and Global Navigation Satellite Systems (GNSS), among others. Apple says, however, the current safety systems are often insufficient and can provide inaccurate road-relative velocity. For example, inertial sensors require the integration of noisy accelerometers which can experience drift, making velocity and slip determinations challenging. GNSS systems such as Global Positioning Systems (GPS) are often unreliable and subject to jammers, which similarly makes the use of GPS challenging for road relative velocity and other computations.
Here’s Apple’s summary of the patent: “Aspects of the present disclosure involve a method for determining a road vehicle velocity and slip angle. The current disclosure presents a technique for identifying a vehicle's velocity and slip angle, in the vehicle's coordinate frame. In one embodiment, two or more sensors are orthogonally located on the underside of the vehicle in order to obtain longitudinal and lateral velocity information for slip angle determination.
“In another embodiment, the two or more sensors can include an array of elements for beam steering and receiver beamforming. Spatial diversity is leveraged in identifying at least a slip angle and/or velocity of the vehicle. Doppler mapping is used as a means for slip angle determination and the clutter ridge of the Doppler map is embraced for identifying the slip angle.”
Of course, Apple files for — and is granted — lots of patents by the U.S. Patent & Trademark Office. Many are for inventions that never see the light of day. However, you never can tell which ones will materialize in a real product.