Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Vehicle diagnosis or maintenance indication
Reexamination Certificate
2003-07-18
2004-11-23
Jeanglaude, Gertrude A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Vehicle diagnosis or maintenance indication
C701S041000, C701S063000, C701S065000, C340S438000, C340S439000, C340S442000
Reexamination Certificate
active
06823245
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention generally relates to an apparatus and program for determining linearity of tire characteristic, which determines the condition of tires of a traveling vehicle in view of linearity of the tire characteristic, and more particularly to a vehicular driving operation apparatus, and a steering control method for steer-by-wire (SBW) vehicles, in which thus-determined condition of the tire is utilized.
Steering gears of vehicles are available in a wide range of variations, such as front-wheel steering gears, rear-wheel steering gears, steering gears with a steering shaft and steerable wheels linked mechanically, and SBW steering gears. Among these types of steering gears, a yaw-rate feedback active steering system known in the art may be provided in order to stabilize vehicle's behavior. The yaw-rate feedback active steering system is designed to compare an actual (actually measured) yaw rate (as an indicator of actual or measured vehicle behavior) with a standard or normative yaw rate (as an indicator of standard or normative vehicle behavior) whereby the directional control for a vehicle is exercised so as to make the actual yaw rate coincide with the standard yaw rate. The standard yaw rate is calculated from a steering angle of the steering shaft, a steering angle (rack position) of the steerable wheels, or other factors, whereas the actual yaw rate is measured with a yaw rate sensor or other vehicle behavior detecting means. The use of this type of active steering system allows the steering gear to provide a stabilized yaw rate in steering (or aiding a driver in steering) the vehicle, and thus serves to effectively stabilize the vehicle.
Utility of the active steering system as described above holds true of cases where the standard yaw rate is greater than the actual yaw rate. However, an adverse effect would be brought about in cases where the vehicle tends to undergo understeer and where the vehicle is on a snowy road or the like, with the actual yaw rate thereof measuring a small value. To be more specific, without reflecting a slipperiness of the road surface, non-linear model of tire characteristic or the like on the control of the steering gear, the steering gear would disadvantageously attempt to make the actual yaw rate closer to the standard yaw rate and to steer the vehicle more so as to increase the steering angle, thus inducing further understeer.
Determination of the slipperiness of road surfaces requires an expensive sensor (e.g., sensors for which the fifth wheel need be installed). The non-linear model of tire characteristic makes the control process complicate. In view of these disadvantages, another approach may be deemed applicable in which the active steering system is disabled in understeer conditions (i.e., standard yaw rate>actual yaw rate); however, this approach would spoil the advantages of the active steering system in cases where the vehicle usually undergoes understeer, with the result that equipment of the active steering system would become ineffectual.
Therefore, it is one exemplary and general object of the present invention to provide an apparatus and program for determining linearity of tire characteristic, in which the condition of tires of a traveling vehicle can be determined using a commonly available sensor and with comparative ease. Another exemplified and more specific object of the present invention is to provide a vehicular driving operation apparatus and steering control method for SBW vehicles, in which the control for a vehicle is exercised utilizing thus-determined condition of the tires.
SUMMARY OF THE INVENTION
The inventors and their colleagues, who have diligently carried on a research to address the above-described problems, focused on the point that comparison between standard vehicle behavior (as indicated by a standard or normative yaw rate) and actual vehicle behavior (as indicated by an actual yaw rate) can be used to determine whether tires stand in a non-linear region or linear region of tire characteristic, and finally completed the present invention.
[Apparatus for Determining Linearity of Tire Characteristic]
According to one exemplified aspect of the present invention, there is provided an apparatus for determining linearity of tire characteristic comprising: a standard vehicle behavior arithmetic unit that calculates a standard vehicle behavior indicator based upon at least one of an operation amount of an operation unit with which a driver of a traveling vehicle performs a steering operation and an actually steered amount of steerable wheels of the traveling vehicle; and a tire characteristic linearity determination unit that compares an actual vehicle behavior indicator with the standard vehicle behavior indicator, to determine whether tires of the traveling vehicle stand in a linear region or in a non-linear region of the tire characteristic. The operation amount of the operation unit, actually steered amount of the steerable wheels, and actual vehicle behavior indicator may be detected by an operation amount detector, a steered amount detector and a vehicle behavior detector, respectively.
In this arrangement, a standard vehicle behavior indicator is calculated based upon detected values transmitted from at least one of the operation amount detector and the steered amount detector, and the resulting standard vehicle behavior indicator is compared with the actual vehicle behavior indicator detected by the vehicle behavior detector, so that determination is made whether the tires stand in the linear region or in the non-linear region. The vehicle behavior indicator includes, but not limited to, a yaw rate as described in one exemplary embodiment which will be described later; for example, a lateral acceleration may be utilized instead. Sensors required for this arrangement, as denoted above by the operation amount detector and/or the steered amount detector, and the vehicle behavior detector, may be selected among general purpose sensors that are inexpensive and thus readily available. Alternatively, sensors with which most vehicles have already been equipped may be used as all or part of the above detectors.
In the non-linear region of tire characteristic, the vehicle is placed in a condition to become unsteerable or undergo understeer even if the steering angle (steering amount) is increased. In contrast, in the linear region of the tire characteristic, the vehicle is in a condition to be steered in an intended direction as the steering angle is increased.
The above tire characteristic linearity determination unit may include: a vehicle behavior deviation change rate arithmetic part that calculates a vehicle behavior deviation by subtracting the actual vehicle behavior indicator from the standard vehicle behavior indicator, and calculates a rate of change of the vehicle behavior deviation; a sign determination part that determines a first sign of one of the vehicle behavior deviation and the rate of change of the vehicle behavior deviation, and a second sign of the actual vehicle behavior indicator; a tire characteristic linearity determination part that determines linearity of tire characteristic, wherein if the first and second signs are both positive and the rate of change of the vehicle behavior deviation is greater than a first prescribed value, and if the first and second signs are both negative and the rate of change of the vehicle behavior deviation is less than a second prescribed value, it is determined that the tires of the traveling vehicle stand in the non-linear region of the tire characteristic.
If the first sign (positive (+)
egative (−)) of the rate of change of the vehicle behavior deviation and the second sign (positive (+)
egative (−)) of the actual vehicle behavior indicator are both positive (+), it is determined that the tires of the traveling vehicle stand in the non-linear region of the tire characteristic when the rate of change of the vehicle behavior deviation is greater than a first prescribed
Kawano Masaaki
Sugitani Nobuo
Tsurumiya Osamu
Jeanglaude Gertrude A.
Merchant & Gould P.C.
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