Fluid-pressure and analogous brake systems – Speed-controlled – Select high wheel speed versus select low
Reexamination Certificate
2002-08-29
2004-02-03
Schwartz, Christopher P. (Department: 3683)
Fluid-pressure and analogous brake systems
Speed-controlled
Select high wheel speed versus select low
C303S137000, C303S113100, C303S122020
Reexamination Certificate
active
06685282
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for operating a reference speed in an anti-lock braking control of an automobile having two or more wheels, and an anti-lock braking control technique on the basis of the reference speed.
2. Description of the Related Art
As a brake control unit for a vehicle such as a two-wheeled vehicle, an anti-lock braking system (ABS) is publicly known which prevents the elongation of a braking distance of the vehicle or the impossibility of the control of the traveling direction of the vehicle with its steering wheel owing to the slipping of the vehicle caused by the locking of a wheel at the time of quick braking or at the time of braking on a slippery road surface.
The anti-lock braking system performs a brake control in order not to lock wheels by detecting the rotational speeds of the wheels at the time of the braking caused by a certain braking operation, and performs the brake control by performing the pressure intensifying control or the pressure reducing control of the brake operation hydraulic pressures to the wheel cylinders of the vehicle on the basis of the detected rotational speeds. To put it concretely, when a wheel is going to be locked, the anti-lock braking system repeats the control of decompressing the brake operation hydraulic pressure to each of the wheel cylinders and the control of pressurizing the brake operation hydraulic pressure according to the wheel rotational speeds to prevent the locking of the wheel. The control of decompressing the brake operation hydraulic pressure is performed by opening the pressure reducing electromagnetic valve on the communicating path of each of the wheel cylinders and each of reservoirs to feed a part of the brake operating liquid, which is fed from each of the master cylinders to each of the wheel cylinders, to each of the reservoirs to decompress the brake operation hydraulic pressure to each of the wheel cylinders. The control of pressurizing the brake operation hydraulic pressure is performed by closing the pressure reducing electromagnetic valve with the brake operating liquid fed from the master cylinder to the wheel cylinder. Moreover, the brake operating liquid fed to each of the reservoirs is compulsively fed to each of the master cylinders by a pump.
When the pressure intensifying control and the pressure reducing control of the brake operation hydraulic pressures to each of the wheel cylinders is performed on the basis of the rotational speed of each of the wheels in the anti-lock braking control, control variables such as acceleration and deceleration of the wheels, a slip ratio, a pseudo car body speed and reference body deceleration are operated by an operation block in an electric control unit (ECU) in the anti-lock braking system. Then, a control block in the ECU performs a brake control in order not to lock the wheels by performing the pressure intensifying control and the pressure reducing control of the brake operation hydraulic pressures to each of the wheel cylinders on the basis of the operated control variables.
The slip ratio, one of the control variables, can be operated from the wheel speed of each of the wheels and a car body speed. When the car body speed and the wheel speed are equal, the slip ratio is 0%. However, the slip ratio becomes larger as the difference between them becomes larger at the time of braking, and it becomes 100% when the wheel is locked before the stop of the car body. However, because the actual speed of the car body cannot be measured, when the slip ratio is operated, it is general that a reference body speed is operated and the slip ratio is operated by supposing the operated reference speed as the car body speed.
For example, in a motorcycle, the reference speed is generated from the wheel speed of an undriven wheel, i.e. the front wheel of the motorcycle, at the time when the anti-lock braking control of the motorcycle is not performed. The reason why the reference speed is generated from the wheel speed of the undriven wheel is that, first, in the state in which the driving wheel of the motorcycle is coupled with an engine, the moment of the inertia of the undriven wheel is sufficiently smaller than that of the driving wheel and is more sensitive to changes of braking torque, and consequently, at an initial step at the time of braking, the reference speed generated from the undriven wheel (front wheel) is closer to the car body speed at that time. Moreover, because the rear wheel being the driving wheel has the possibility of a rapid slip at the time of acceleration, the reference speed generated on the basis of the wheel speed of the front wheel is closer to the actual car body speed.
On the contrary, at the time of the anti-lock braking control, the reference speed having a larger value among the two values of the reference speeds generated on the basis of each of the wheel speeds of the front wheel and the rear wheel (driving wheel), namely the reference speed generated on the faster wheel speed among the wheel speeds of the front wheel and the rear wheel, is selected. The selection is generally called as the so-called select-high (or high-select), and is a method for operating a reference speed based on a publicly known technical basis. The method is regarded as the most effective method for approximating the progress of the reference speed to the actual car body speed to grasp the slip ratio as accurately as possible.
Now, particularly in a motorcycle, a phenomenon easily occurs which the rear wheel of the motorcycle floats at the time of braking. Among motorcycles, a vehicle having a larger ratio of the height of the center of gravity of the vehicle to a distance between the wheel shafts of the front wheel and the rear wheel has the inclination that the rear wheel of the vehicle easily floats. Then, when only the front wheel of such a motorcycle is braked while traveling on a road surface having a large coefficient of friction (the so-called high &mgr; road surface), the rear wheel of the motorcycle easily floats in the air. From the point of view of achieving the safety of a traveling vehicle, also, it is desired to prevent such lifting of the rear wheel by detecting the lifting of the rear wheel to perform, for example, a suitable brake control of the front wheel.
However, for example, if braking is performed only to the front wheel and the rear wheel floats during the anti-lock braking control of the front wheel, the lifting of the rear wheel removes the ground resistance to the rear wheel to decrease the deceleration of the rear wheel rapidly. Consequently, if the anti-lock braking control is executed on the basis of the reference speed operated by following the wheel speed of the rear wheel selected in accordance with the above-mentioned select-high, the reference speed becomes higher than the actual car body speed at the time of the lifting of the rear wheel. Thereby, the situation is judged to be one in which a wheel is slipping relatively. Then, although the wheels are not slipping, a pressure reducing control of a wheel cylinder is performed. Consequently, the problem in which the braking feeling of a brake is spoiled is produced.
Accordingly, it is possible to prevent the situation in which a reference speed becomes higher than an actual car body speed by taking a basis on the reference speed operated to follow the wheel speed of the front wheel selected by a method, the so-called select-low, to select the value of a reference speed being a smaller one among the values of the reference speeds of the front wheel and the rear wheel at the time of the lifting of the rear wheel. However, in this case, the selected reference speed becomes lower than the actual car body speed in turn. Consequently, there is the possibility of occurring the problem in which extreme changes of vehicle stability occur in the time of traveling on a low &mgr; road surface particularly.
SUMMARY OF THE INVENTION
The present invention was made in consideration of such situations. It is an objec
Bosch Automotive Systems Corporation
Priest & Goldstein PLLC
Schwartz Christopher P.
Torres Melanie
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