Starting from an acceleration signal, representative of a radial acceleration undergone by a portion of a crown region of said tyre due to the rolling of said tyre on a rolling surface, the trend of the first derivative of the radial acceleration is determined at a portion representative of the interaction of the tyre with a water layer. From the trend of the first derivative of the radial acceleration, it is determined at least one first parameter representative of an aquaplane condition of the tyre on the basis of a comparison between a first maximum and a second maximum of the first derivative at the portion representative of the interaction between tyre and water layer.

A road surface state determination device includes a tire-side device and a vehicle-body-side system. The tire-side device is attached to each of a plurality of tires included in a vehicle. The vehicle-body-side system is included in a body of the vehicle. The tire-side device may output a detection signal corresponding to a magnitude of vibration of the tire. The tire-side device may sense the detection signal and generate road surface data indicative of a road surface state appearing in a waveform of the detection signal. The tire-side device may transmit the road surface data. The vehicle-body-side system may perform bidirectional communication with the tire-side device and receive the road surface data. The vehicle-body-side system may determine the road surface state of a road surface on which the vehicle is traveling based on the road surface data.

A tire system includes a tire-side device and a vehicle-body-side system. The tire-side device may be attached to a tire included in a vehicle. The vehicle-body-side system may be attached to a body of the vehicle. The tire-side device may output a detection signal corresponding to each of a plurality of types of detection targets. The tire-side device may perform processing of the detection signal and generate the data related to the detection target. The tire-side device may perform bidirectional communication with the vehicle-body-side system and transmit the data to the vehicle-body-side system. The vehicle-body-side system may perform bidirectional communication with the tire-side device and receive the data. The vehicle-body-side system may acquire the detection result for the detection target based on the data.

A vehicle body side system is provided with a second data communication unit that performs bidirectional communication with a tire side device and receives road surface data and measurement data transmitted from a first data communication unit, a road surface determination unit that determines the road surface condition of a road surface on which a vehicle travels based on the road surface data, a reception strength measurement unit that measures the reception strength of the measurement data, and a transmission angle setting unit that stores the reception strength of the measurement data during one rotation of a tire, sets as a transmission angle, a presence angle when the reception strength of the measurement data during one rotation of the tire is high, and transmits data indicating the transmission angle to the tire side device via the second data communication unit. In addition, a control unit causes the first data communication unit to transmit the road surface data when the presence angle becomes the transmission angle.

A system calibrates a function of a tire friction of a vehicle traveling on a road from motion data including a sequence of control inputs to the vehicle that moves the vehicle on the road and a corresponding sequence of measurements of the motion of the vehicle moved by the sequence of control inputs. The system updates iteratively the probability distribution of the tire friction function until a termination condition is met, wherein, for an iteration, the system samples the probability distribution of the tire friction function, determines a state trajectory of the vehicle to fit the sequence measurements according to the measurement model and the sequence of control inputs according to the motion model including the sample of the tire friction function, and updates the probability distribution of the tire friction function based on the state trajectory of the vehicle.

A tire mount sensor detects a road surface condition such as a type of a road surface and a road surface , and transmits road surface data indicating a detection result to a communication center. The communication center collects road surface data more precisely, and the vehicle receives the more precise road surface data from the communication center. Based on received more precise road surface data, the risk of the vehicle is determined. Thus, the road surface condition is detected using the tire mount sensor, so that the road surface condition is detected without braking. Accordingly, it is possible to detect the road surface condition with high frequency, so that the road surface condition is detected in wider area, and it is possible to perform the control more appropriately for avoiding the risk based on the road surface condition during a travel.

A method for evaluating the firmness of the ground on which is running a vehicle equipped with at least one mounted assembly having a radial stiffness k.sub.radial comprising a tyre casing having a crown, two sidewalls and two beads, equipped with a sensor sensitive to the circumferential curvature and positioned in line with the crown, comprises the following steps: Estimating a value of the curvature .sub.A of the tire casing corresponding to first steady-state conditions of the tire casing in contact with the ground; and Evaluating the relative firmness of the ground with respect to the radial stiffness k.sub.radial of the mounted assembly as being a function of the value of the curvature .sub.A of the tire casing.

A road surface information collection device includes a first sampling unit that samples acceleration sensor's detection results with a first sampling cycle to obtain first sampling data, a position calculator that calculates an acceleration sensor's rotational position based on changes in first sampling data, a second sampling unit that is activated based on a condition that the acceleration sensor is positioned within a first predetermined range including a back side of a point on the tire in contact with the ground, and that samples detection results of the acceleration sensor with a second sampling cycle shorter than first sampling cycle to obtain second sampling data as the road surface information, a speed calculator that detects a rotation speed of the tire based on changes in the first sampling data, and a first predetermined range determination unit that changes the first predetermined range in accordance with the rotation speed of tire.

A road surface state estimation device includes a tire-side device and a vehicle-body-side system. The tire-side device is disposed in a tire. The vehicle-body-side system is disposed in a vehicle body. The tire-side device outputs a detection signal corresponding to a magnitude of vibration of the tire, generates road surface data based on the detection signal, and performs data communication with the vehicle-body-side system. The vehicle-body-side system acquires information related to the road surface state, performs the data communication with the tire-side device, transmits vehicle-body-side information indicating that the change in the road surface state occurs to the tire-side device when determining that a change in the road surface state occurs based on the information related to the road surface state, and estimates the road surface state based on the road surface data received by the second transceiver.

In a braking performance evaluation method including the steps of acquiring a tire ground contact pressure distribution, acquiring a sliding friction coefficient table, and calculating a friction force of an entire tire using a brush model having a function representing the tire ground contact pressure distribution and the sliding friction coefficient table, the step of acquiring the tire ground contact pressure distribution includes the step of acquiring a first ground contact pressure distribution on a road surface on which no water film is present via actual measurement or calculation and the step of acquiring a second ground contact pressure distribution by applying reduction in a ground contact pressure due to a water film intruded between the tire and the road surface to the first ground contact pressure distribution and using the second ground contact pressure distribution as the tire ground contact pressure distribution used for the calculating.