Measuring and testing – Tire – tread or roadway
Reexamination Certificate
2000-09-20
2003-07-15
Oen, William (Department: 2855)
Measuring and testing
Tire, tread or roadway
Reexamination Certificate
active
06591670
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for estimating the air pressure of a tire, and in particular, to a device for detecting a wheel speed signal frequency from the wheel speed signal of a wheel, and to a device for estimating the state of air pressure of a tire from the wheel speed frequency.
Further, the present invention relates to a device for estimating the state of air pressure of a tire, and in particular, to a device for estimating the state of air pressure of at least one of the left and right wheels from the vibration frequencies of the wheel speed signals of the left and right wheels which are connected by a mechanical element.
2. Description of the Related Art
Devices for estimating the air pressure of a tire inform the driver of abnormalities or the like in a tire of a vehicle. In addition to tire air pressure estimating devices which directly detect the air pressure of a tire, there is the tire air pressure estimating device disclosed in Japanese Patent Application Laid-Open (JP-A) No. 5-133831. The tire air pressure estimating device disclosed in JP-A-5-133831 focuses on the correlation between the air pressure of the tire and the resonance frequency of the tire. The resonance frequency of the tire is detected by a fast Fourier transform (FFT) of the vibration component of the wheel speed. When the resonance frequency is less than a predetermined value, it is judged that there is an air leak in the tire such as a puncture in the tire, and a warning is given.
Further, dynamic system diagnostic devices such as the following have been disclosed in JP-A-7-98268 and JP-A-10-187236. On the basis of the response output vector of the dynamic system, an overall disturbance vector is estimated as the sum of the external disturbance vector applied from the exterior of the dynamic system and the internal disturbance vector generated by problems within the dynamic system. The internal state amount vector of the dynamic system is estimated. By computing the cross-correlation between the estimated overall disturbance vector and the internal state amount vector, the component relating to the internal disturbance is separated from the overall disturbance vector. From this separated component relating to the internal disturbance, the corresponding portion of the dynamic system is diagnosed as a malfunctioning portion. For example, a decrease in the air pressure can be judged by using such a diagnostic device.
In this case, when the dynamic system is a wheel including a tire, the disturbance vector applied from the exterior of the wheel is a vibration input which is inputted to the wheel resonance system. If a malfunction within the tire is an internal disturbance vector generated by a decrease in air pressure, it can be judged that the air pressure of the tire has decreased.
However, the method of computing the resonance frequency in the tire air pressure estimating device disclosed in JP-A-5-133831 is complex.
Further, when the air pressure is determined by using the above-described diagnostic devices (of JP-A-7-98268 and JP-A-10-187236), there may be included a response output in which the magnitude of the response output vector becomes suddenly large, or a response output in which periodic changes are not expressed markedly. If it is determined that the air pressure has dropped on the basis of an output response which includes a response output whose magnitude has suddenly become large, the effect of the response output which has suddenly become large will be too large, and the existing, periodic response output will be hidden in the response output which became large suddenly. Accordingly, the estimated values of the physical amounts for determining the decrease in the air pressure will vary, and the accuracy of judging a decrease in the air pressure will be poor.
Further, conventionally, as described above, the relationship between the vibration frequency of the wheel speed signal and the tire air pressure is constant, and the tire air pressure is estimated by using this relationship. For example, in the tire air pressure estimating device disclosed in Japanese Patent No. 2899741, the tire air pressure is estimated on the basis of the frequency (vibration frequency) of the vibration of the wheel speed signal. Thus, the air pressure of the tire can be estimated without requiring a device for directly detecting the air pressure such as a pressure sensor.
However, in accordance with the air pressure estimating device described above, although the tire air pressure of a non-drive wheel can be estimated accurately, when the left and right wheels are connected by mechanical elements of a drive system in the case of drive wheels, the vibration component transferred from the mechanical elements and unrelated to the tire air pressure is included in the wheel speed signal. Thus, the air pressure of the tire cannot be estimated accurately.
Here, in the invention disclosed in JP-A-8-230422, by using the fact that the vibration components of the drive system transmitted from the mechanical elements are included as same-phase components in the wheel speed signals of the left and right wheels, the tire air pressure is estimated on the basis of a signal corresponding to the difference between the wheel speed signals of the left and right wheels (a signal in which the vibration component of the drive system is removed).
Namely, the above-described invention utilizes the method of least squares and the difference in the estimated disturbances of the left and right drive wheels at the time a predetermined parameter is varied, which estimated disturbances are obtained by an equation of motion of the left and right drive wheels and an equation of state of the left and right drive wheels, and estimates the aforementioned parameter, and estimates the tire air pressure which offsets the vibration component of the drive system.
However, in accordance with the above-described invention, in this device for estimating the tire air pressure of the drive wheels, the amount of computation is larger and more complex than that for non-drive wheels which are not affected by the vibration of the drive system. For example, in the above-described publication (the first embodiment thereof), the order of the matrix of the least squares method used in the tire air pressure estimating device of the non-drive wheels is 2. However, the order of the matrix of the least squares method used in the tire air pressure estimating device of the drive wheels is 4. Thus, the amount of computation which must be performed is twice as much or more. In this way, the computation processing for estimating the tire air pressure is complex.
SUMMARY OF THE INVENTION
In view of the aforementioned, a first object of the present invention is to provide a wheel speed signal frequency detecting device in which the frequency of a wheel speed signal can be determined easily, and to provide a device for estimating a tire air pressure state with high accuracy by the frequency of the wheel speed signal.
Further, in view of the aforementioned, a second object of the present invention is to provide a device for estimating a tire air pressure state by a simple computation processing.
In order to achieve the above-described first object, a first aspect of the present invention is: a device for estimating a state of tire air pressure, comprising: a wheel speed detecting device which detects a wheel speed of a wheel including a tire; a reference value setting device which sets, as a reference value, an amplitude center of the wheel speed signal outputted from the wheel speed detecting device; and a tire air pressure state estimating device which estimates a state of air pressure of the tire on the basis of a number of times the wheel speed signal crosses the reference value.
In accordance with the present invention, the wheel speed, such as the rotational speed of a wheel including a tire, is detected by a wheel speed detecting device, and the wheel speed detecting device outputs a wheel spee
Asano Katsuhiro
Umeno Takaji
Kabushiki Kaisha Toyota Chuo Kenkyusho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Oen William
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