Fluid-pressure and analogous brake systems – Speed-controlled – Pressure reapply control
Reexamination Certificate
1999-09-29
2001-04-17
Butler, Douglas C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Pressure reapply control
C303S177000, C303S156000
Reexamination Certificate
active
06217134
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anti-skid control system for an automotive vehicle, wherein brake pressure in each wheel brake cylinder is controlled in accordance with pressure control modes including a pulse pressure increase mode.
2. Description of the Related Arts
Various anti-skid control systems have been proposed heretofore to prevent a wheel from being locked during a braking operation of a vehicle. For example, Japanese Patent Laid-open Publication No.8-150918 discloses an anti-skid control system which is adapted to compare a wheel acceleration with a vehicle acceleration at a predetermined time, and adjust a pressure increasing rate of braking pressure, based upon the result of comparison. According to that publication, in view of a prior anti-skid control system as disclosed in Japanese Patent Laid-open Publication No.4-345567, which was aimed to provide an appropriate pressure increasing rate in accordance with the slip rate under such a condition as the coefficient of friction of a road (hereinafter, abbreviated as a road &mgr;) or the like is constant, thereby to achieve an ideal braking force control, it was proposed to solve such a problem that the ideal braking force control could not necessarily be achieved by that prior anti-skid control system, when the condition such as the coefficient of friction of the road was varied.
According to the anti-skid control system as disclosed in the aforementioned Japanese Patent Laid-open Publication No.8-150918, however, when a vehicle travels on a rough road, which includes unpaved road, stone pavement, snow road or the like, it will not be easy to perform the anti-skid control operation appropriately, because not only the road &mgr; will vary, but also the vehicle wheels will vibrate. This is because the detected wheel acceleration will include the variation due to disturbance caused by change of the road surface, so that comparing the wheel acceleration with the vehicle acceleration at the predetermined time, i.e., at the specific time determined in advance will result in the comparison between the wheel acceleration and the vehicle acceleration including the variations caused by the disturbance of the road surface.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an anti-skid control system for performing the braking force control, appropriately and effectively, even when a vehicle is traveling on a rough road.
In accomplish the above object, the anti-skid control system includes wheel brake cylinders which are operatively mounted on wheels of the vehicle, respectively, a pressure generator which is adapted to pressurize brake fluid in response to operation of a manually operated member to generate a hydraulic braking pressure, and supply the hydraulic braking pressure to each of the wheel brake cylinders, and a pressure control device which is disposed between the wheel brake cylinders and the pressure generator. The pressure control device is adapted to set at least a pressure decrease mode for decreasing the hydraulic braking pressure and a pulse pressure increase mode for intermittently increasing the hydraulic braking pressure, with a pressure increasing signal provided in accordance with the braking condition of the vehicle, to control the hydraulic braking pressure in each of the wheel brake cylinders. A wheel acceleration detection device is provided for detecting a wheel acceleration of each wheel of the vehicle, and a vehicle acceleration detection device is provided for detecting a vehicle acceleration of the vehicle. A wheel speed peak detection device is provided for detecting peaks of the wheel speed in the pulse pressure increase mode continuously on the basis of a variation of the wheel acceleration detected by the wheel acceleration detection device relative to the vehicle acceleration detected by the vehicle acceleration detection device. And, a pulse pressure increase mode adjusting device is provided for setting the time when each peak of the wheel speed was detected by the wheel speed peak detection device as a rise timing of the pressure increasing signal in the pulse pressure increase mode, and adjusting a time period for which the pressure increasing signal outputs, on the basis of a variation of the rotating condition of the wheel at the time when the peak of the wheel speed was detected.
Preferably, the wheel acceleration detection device is adapted to differentiate the wheel speed to obtain the wheel acceleration, and the vehicle acceleration detection device is adapted to calculate an estimated vehicle speed on the basis of the wheel speed, and differentiate the estimated vehicle speed to obtain the vehicle acceleration. According to the system as described above, peaks of the wheel speed in the pulse pressure increase mode are detected continuously on the basis of a variation of the wheel acceleration relative to the vehicle acceleration, and the time when each peak of the wheel speed was detected is set as a rise timing of the pressure increasing signal in the pulse pressure increase mode, and a time period for which the pressure increasing signal outputs is adjusted, on the basis of a variation of the rotating condition of the wheel at the time when the peak of the wheel speed was detected. As a result, the pulse pressure increase control can be performed in such a manner that immediately after the braking torque is applied to the wheel, the tire torque will be applied to it. Therefore, the braking force can be applied properly to the wheel properly without being influenced by the wheel vibration. As for factors for determining the rotating condition of the wheel, may be employed the variation of wheel speed, wheel acceleration, or a slip rate, based on which the output time of the pressure increasing signal can be adjusted.
In the anti-skid control system as described above, therefore, the pulse pressure increase mode adjusting device may be adapted to adjust the time period for which the pressure increasing signal outputs, on the basis of a ratio of a first integrated value of a difference obtained by subtracting the vehicle acceleration from the wheel acceleration, to a second integrated value of a difference obtained by subtracting the wheel acceleration from the vehicle acceleration. For instance, the time period of the pressure increasing signal may be set to be shorter, as the ratio of the first integrated value to the second integrated value is reduced.
The anti-skid control system as described above may further include a wheel speed detection device for detecting wheel speeds of the wheels of the vehicle, a vehicle speed detection device for detecting a vehicle speed of the vehicle, and a slip rate calculation device for calculating a slip rate on the basis of the wheel speeds detected by the wheel speed detection device and the vehicle speed detected by the vehicle speed detection device. And, the pulse pressure increase mode adjusting device may be adapted to adjust the time period for which the pressure increasing signal is output, on the basis of the slip rate calculated by the slip rate calculation device at the time when the peak of the wheel speed was detected. For instance, the time period of the pressure increasing signal may be set to be shorter, as the slip rate calculated by the slip rate calculation device is close to the slip rate at a peak of the coefficient of friction of the road.
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Abe Yasuhiro
Kato Toshihisa
Sakane Shinsuke
Aisin Seiki Kabushiki Kaisha
Burns Doane , Swecker, Mathis LLP
Butler Douglas C.
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