Apple has Won a Project Titan Patent relating to Friction Forces of a Tire Surface that Controls a Vehicle
Today the U.S. Patent and Trademark Office officially granted Apple a patent that relates to Project Titan and more specifically to systems and methods for determining a friction parameter, such as a maximum available traction force or a friction coefficient of a tire/surface interface, to control operation of a vehicle.
Apple's patent background notes that a tire generates a traction force through compression and expansion of the tire body and via its interaction with an underlying surface (e.g., road). During acceleration, deceleration, and turning of a vehicle, the tire will slide with respect to the surface in addition to rolling, and this sliding is referred to as wheel slip. The amount of longitudinal sliding may be expressed as a slip ratio, which is the relative difference between the tire's rotational velocity and the achieved translational velocity. The amount of lateral sliding may be expressed as a slip angle, which is an angular difference between the direction that the tire is pointing and the direction that the vehicle is moving. The traction force generated by the tire is a non-linear function of the slip ratio and the slip angle.
Apple's granted patent covers a method for controlling a vehicle having a set of tires. The method includes applying torque to one or more tires from the set of tires to cause the vehicle to move along a surface, reducing an amount of downward force applied to the surface by a first tire from the set of tires using an active suspension component, and subsequent to reducing the amount of downward force applied to the surface by the first tire, actuating the first tire to control a dynamic response of the first tire relative to the surface. The method also includes determining, while actuating the first tire, a traction force of the first tire relative to the surface at each of multiple values for the dynamic response of the first tire relative to the surface, determining a maximum available traction force based on the multiple values of the dynamic response and corresponding values for the traction force, determining a friction parameter based on the maximum available traction force, and controlling an operation of the vehicle based on the friction parameter.
Apple's patent FIG. 3A is a schematic that illustrates and example of a downward force being distributed from a first tire to the other tires of the vehicle; FIGS. 7A-7D are illustrations that show examples in which a yaw moment caused by a reduced downward force applied to one of the tires of the vehicle is opposed by counter-steering; FIG. 5 is a schematic illustrating example of the various measurements, velocities, and forces that may be sampled to determine a slip ratio and a maximum available traction force.
Apple's patent FIGS. 2A and 2B above are schematics that illustrate an example of a downward force being reduced from a first tire and being distributed to a second tire.
Car mechanics and engineers will appreciate reviewing the details behind Apple's granted patent 10,988,142 here.