Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Indication or control of braking – acceleration – or deceleration
Reexamination Certificate
2001-06-21
2003-07-29
Louis-Jacques, Jacques H. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Indication or control of braking, acceleration, or deceleration
C701S078000, C701S082000, C303S155000, C303S157000
Reexamination Certificate
active
06600987
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an improvement of determining a road-wheel vibration of an automotive vehicle that is caused by a road surface condition, and especially, to an anti-skid braking system that executes a skid control procedure depending on the road-wheel vibration determined by a road-wheel vibration determining system.
2. Description of the Related Art
As is generally known, there have been proposed various anti-skid braking systems for automotive vehicles (hereinafter, referred to as “ABS”) that prevent a skid of the road wheel during a braking in order to provide a maximum effective braking. The ABS executes a skid control by regulating a pressure of each wheel-brake cylinder mounted to each of the road wheels, depending on a pressure-reduction threshold that is calculated based on a wheel speed of each of the road wheels in a vehicle traveling condition. For instance, when the wheel speed becomes lower than a pressure-reduction threshold value, that is, the road wheel tends to be locked, the ABS executes a pressure-reduction procedure of the wheel-brake cylinder pressure. In contrast, when the wheel speed becomes higher than the pressure-reduction threshold value, the ABS executes a pressure build-up procedure so as to adjust the wheel speed toward the pressure-reduction threshold value. By repeating the pressure-reduction procedure and the pressure build-up procedure, a minimum braking distance can be provided. When skid control is executed in a bad road surface condition, the bad road surface condition causes a road-wheel vibration. Thus, if the ABS executes the skid control depending on the same pressure-reduction threshold value that is calculated in a normal road surface condition, the wheel speed fluctuates around the pressure-reduction threshold at a high-frequency that causes a frequent execution of the pressure-reduction procedure. Thereby, a braking distance tends to be long.
As a measure of the foregoing problem, there have been proposed another type of anti-skid braking system that sets the pressure-reduction threshold at a lower value as compared to a normal value set in the normal road surface condition when the bad road surface condition is determined. According to a conventional manner, the bad road surface condition is determined when the wheel speed cycle becomes lower than a predetermined value.
However, during the skid control, the road-wheel vibration is sometimes caused by a drive-train vibration. In this case, when the bad road surface condition is determined by the conventional manner, the drive-train vibration might be determined to be a road-wheel vibration that is caused by the bad road surface condition. Particularly, in a low coefficient of friction of the road surface condition (hereinafter, a coefficient of friction of the road surface is referred to as “&mgr;”), if the pressure-reduction threshold is set at the lower value due to such determination, the pressure-reduction procedure tends to be executed late as a result of setting the pressure-reduction threshold at the lower value. Thereby, a skid of the road wheel might occur. Furthermore, since a range of a pressure-reduction volume and a pressure build-up volume tend to be large because of such late execution of the pressure-reduction procedure, a hunting of an execution of the skid control may occur.
A torque of an engine is transmitted from an engine to driving wheels via a drive shaft and a differential gear. When the ABS executes the pressure build-up procedure and the pressure-reduction procedure while the torque is accelerating the automotive vehicle, a phase shift of the torque is sometimes made due to a generation of an interference of the torque among the engine, the drive shaft, the differential gear and the driving wheel that causes a resonance of 6-7 Hz. Furthermore, in case of a four-wheel drive vehicle, which has a strong constraint force between a front axle and a rear axle, if an inverse phase of the torque is generated by an inverse timing of executing the pressure build-up procedure between the front axle and the rear axle, a torsional resonance is generated on the drive shaft.
In order to solve aforementioned problem, there has been proposed the another type of ABS having a vibration determining system that determines whether the road-wheel vibration is caused by the bad road surface condition, or the road-wheel vibration is caused by the drive-train vibration. One such vibration determining system is disclosed in a Japanese patent publication (koukai) No. 7-257347. According to the publication, the road-wheel vibration is detected based on a wheel acceleration cycle and a wheel acceleration amplitude, and then, the road-wheel vibration is determined whether the road-wheel vibration is caused by the bad road surface condition, or the road-wheel vibration is caused by the drive-train vibration based on a wheel acceleration. When the ABS determines that the road-wheel vibration is caused by the bad road surface condition, the ABS sets the pressure-reduction threshold at the lower value as compared to the normal value set in the normal road surface condition. Thereby, a tendency of the road wheel to be locked caused by the late execution of the pressure-reduction proceeding is avoided. When a drive-train vibration is identified, the pressure-reduction threshold is not changed.
However, since a change of the wheel speed varies in a bad road surface condition, the same wheel acceleration generated in a case where the drive-train vibration is causing the road-wheel vibration is sometimes made in the bad road surface condition. In this case, according to the conventional manner, since the road-wheel vibration is determined based on the wheel acceleration, the ABS determines that the road-wheel vibration is caused by the drive-train vibration, and thus, the pressure-reduction threshold is not changed. Thereby, an insufficient braking force may be made.
In case of the four-wheel drive vehicle, during a traveling in a four-wheel drive state, the ABS might determine that the road-wheel vibration is caused by the bad road surface condition, when the torsional resonance is generated on the drive shaft by a braking. As a result of such determination, the ABS sets the pressure-reduction threshold at the lower value, and the road wheel tends to be locked that causes an instability of the vehicle. Thereby, a late pressure-reduction procedure, which causes a tendency of the range of the pressure-reduction volume and the pressure build-up volume to be wide, is executed, and therefore, the hunting of the execution of the skid control that would encourage the drive-train vibration may occur. According to the related art disclosed in the publication, although the ABS sets the pressure-reduction threshold at the lower value when the bad road surface condition is determined, the minimum braking distance cannot be provided by simply setting the pressure-reduction threshold at the lower value. Moreover, although the ABS disclosed in the related art sets the pressure-reduction threshold at a higher value as compared to the normal value when the drive-train vibration is determined, the drive-train vibration cannot be inhibited due to a repeated execution of the pressure-reduction procedure and the pressure build-up procedure.
SUMMARY OF THE INVENTION
Accordingly, in view of above described problems, a principal object of the present invention is to provide an improved method of determining a road-wheel vibration and a method of executing an anti-skid control having a road-wheel vibration determining method, and an anti-skid control system using the same method, by which the road-wheel vibration is accurately determined, whether a bad road surface condition causes the road-wheel vibration or a drive-train vibration causes the road-wheel vibration.
Another object of the present invention is to provide an anti-skid braking system that provides a maximum effective braking with a minimum braking distance in a bad road surface condition.
Stil
Louis-Jacques Jacques H.
Unisia Jecs Corporation
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