Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication
Reexamination Certificate
1999-07-28
2001-10-23
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
C701S036000, C701S073000, C701S074000, C303S148000, C303S150000, C180S197000
Reexamination Certificate
active
06308115
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vehicle running condition judgment device, and in particular to a device for judging a road surface condition and a vehicle under limit condition, using a vehicle motion model.
2. Description of the Related Art
A road surface condition judgment device is mounted on a vehicle, and judges a road surface condition while the vehicle is running. A judgment result on the road surface condition obtained on such a device is used in electronic running control. For enhanced driving safety, judgment with improved accuracy on road surface condition has been desired. In particular, for various driving control in a four-wheel steering system and a vehicle spin prevention system, accurate comprehension of road surface condition is critical.
Japanese Patent Laid-open No. Hei 8-119131 discloses a device for detecting a slippery state of a road surface. Based on values obtained from various sensors (sensor values) and pre-stored tire characteristics substituted into a vehicle motion model (an equation of state), the device estimates reference state quantity (e.g., a vehicle lateral acceleration). Then, a difference (a residual error) between the reference state quantity and detected state quantity based on a sensor value (e.g., a vehicle lateral acceleration) is calculated, and a predetermined number of such data items on the difference are ordered in time series to form reference difference time series data. Meanwhile, a plurality of estimated difference time series data items are prepared according to respective road surface conditions. Then, the pattern of the reference difference time series data is compared with those of the plurality of estimated difference time series data items to see which data item shows the closest pattern to that of the reference difference time series data for judgment on current road surface condition.
Japanese Patent Laid-open No. Hei 9-311042 discloses a device for estimating a vehicle slip angle using a vehicle motion model, similar to the above. In this device, a lateral acceleration estimated from a cornering performance model is compared with a detected lateral acceleration for judgment on the road surface condition, based on which tire characteristics are determined. The determined tire characteristics are in turn used in estimation of a vehicle slip angle. For estimation of a vehicle slip angle, a feed back control method utilizing an observer is employed, details of which are also disclosed in Japanese Patent Laid-open No. Hei 3-122541. In this method, a state estimation technique, one of the modern control theories, is utilized in detection of a vehicle slip angle.
A conventional device disclosed in the above mentioned Japanese Patent Laid-open No. Hei 8-119131, however, aims at detection of slippery state of a road surface only at the initial stage of a vehicle's turning before spinning, and can therefore be used, in principle, for judgment on road surface condition only at the initial stage of a vehicle's turning. After all, this device can not be used when the road surface condition varies while the vehicle is turning, and the road surface condition in such circumstances can therefore not be detected. Specifically, in the above conventional device, phase deviation is caused, as the vehicle begins slipping, between a modeling result and an actual value obtained on a sensor. As such, the reference difference time series data matches to none of the estimated difference time series data, resulting in failure of accurate judgment on road surface condition. In other words, judgment on road surface condition by the above conventional device is achievable only at the initial stage of a vehicle's turning.
Also, various conventional devices are incapable of correct determination on road surface condition when a vehicle runs under various running conditions. For example, there has conventionally been a problem that judgment on road surface condition is applicable only at the initial stage of a vehicle's turning.
SUMMARY OF THE INVENTION
The present invention has been conceived to overcome the above problems and aims to achieve accurate estimation of road surface conditions. Another object of the present invention is to achieve detection of a change in road surface condition, if such a change occurs during a vehicle's turning. A still further object of the present invention is to achieve prompt and reliable detection of a vehicle in a limit running condition.
In order to achieve the above objects, according to the present invention, there is provided a vehicle running condition judgment device, comprising detection means for detecting a state quantity concerning motion of a vehicle; memory means for storing non-linear tire characteristics for each of a plurality of assumed road surfaces; slip angle estimation means for estimating a vehicle slip angle for each of the plurality of assumed road surfaces based on the state quantity and the non-linear tire characteristics; feedback compensation means for compensating the vehicle slip angle for each of the plurality of assumed road surfaces by compensating a currently estimated vehicle slip angle for each of the plurality of assumed road surfaces based on a current state quantity and a last vehicle slip angle having been estimated for respective assumed road surfaces; and judgment means for judging current road surface condition based on the vehicle slip angle compensated by said feedback compensation means.
Non-linear tire characteristics for respective assumed road surface conditions (e.g., a dry road and a snow covered road) are pre-stored for later use in estimation of a vehicle slip angle. Comparison between an estimation value (or other physical quantity calculated based on the estimation value) and an actual detection value will lead to determination on current road surface condition. Data on the estimated slip angle is compensated in the feed-back compensation means before being output. With this arrangement, a road surface condition can be accurately determined, avoiding phase deviation, even when the condition is changed while the vehicle is turning.
Further, according to one aspect of the present invention, non-linear tire characteristics show non-saturated characteristics. With non-saturated characteristics, an estimation value can be prevented from being oscillated.
According to another aspect of the present invention, the judgment means comprises estimation angular velocity calculation means for calculating a vehicle slip angular velocity for each of the plurality of assumed road surfaces as an estimation angular velocity based on the vehicle slip angle compensated by said feed-back compensation means for each of the plurality of assumed road surfaces, detection angular velocity calculation means for calculating a vehicle slip angular velocity as a detection angular velocity based on the state quantity, and road surface condition judgment means for judging a current road surface condition through comparison between the detection angular velocity and the estimation angular velocity.
With this arrangement, estimation angular velocities are obtained based on vehicle slip angles for the respective assumed road surfaces. The current road surface condition is determined depending on which of the estimated angular velocities is closest to the actual angular velocity.
Still further, according to another aspect of the present invention, the judgment means comprises estimation lateral acceleration calculation means for calculating a lateral acceleration for each of the plurality of assumed road surfaces as an estimation lateral acceleration based on the non-saturated tire characteristics and the vehicle slip angle compensated by said feed-back compensation means for each of the plurality of assumed road surfaces; and road surface condition judgment means for judging a current road surface condition through comparison between a detected lateral acceleration and the estimation lateral acceleration.
With
Asano Katsuhiro
Itoh Takayuki
Nishio Akitaka
Tozu Kenji
Yamaguchi Hiroyuki
Kabushiki Kaisha Toyota Chuo Kenkyusho
Louis-Jacques Jacques H.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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